Take the Katana, melt it down, slap another chunk of metal in there and turn it into a Broadsword... 
Unfortunately Katana is always going to be very weak in PvP because:
#1: It's got low burst damage.
#2: It's all Lethal damage, which is very highly resisted.
#3: It's got no mez effects other than Knockdown, which every decent PvPer will have protection against.
I've a 50 Katana/Regen myself and it's an awesome PvE soloer toon, but the combo is completely pants in PvP because you simply won't be able to kill anybody unless they're AFK. You can build it to stalemate just about any other melee toon and most ranged toons, but not to actually kill anything.
The only toons I've ever managed to kill with my Kat/Regen in PvP are squishies that simply don't know how to kite, or the few Melee toons that make it a point of honour to stay toe-to-toe until one of you drops.
I also have a level 50 Katana/Regen and I'm mainly an ardent PvE'er, but recently I've started to move into the PvP arena with him, and he's doing ok, considering I have no idea what I'm doing most of the time though. I'll agree it's probably the most fun toon I've ever had PvE and I was able to tank the Rikti Mothership raid we had the other day, although with my build I couldn't have held aggro if you'd put a gun to my head, I was able to take the Alpha and the majority of the pylons attacks without any problems.
With regards to PvP builds, one of my SG came up with this one, be warned it'll cost ya silly money though
Hero Plan by Mids' Hero Designer 1.21
http://www.honourableunited.org.uk/mhd.php
kiddo: Level 50 Magic Scrapper
Primary Power Set: Katana
Secondary Power Set: Regeneration
Power Pool: Fitness
Power Pool: Leadership
Power Pool: Leaping
Power Pool: Speed
Ancillary Pool: Body Mastery
Hero Profile:
------------
Level 1: Sting of the Wasp
(A) Crushing Impact - Accuracy/Damage: Level 40
(3) Crushing Impact - Accuracy/Damage/Endurance: Level 40
(3) Crushing Impact - Accuracy/Damage/Recharge: Level 40
(9) Crushing Impact - Damage/Endurance/Recharge: Level 40
(11) Crushing Impact - Damage/Recharge: Level 40
(40) Accuracy IO: Level 50
Level 1: Fast Healing
(A) Numina's Convalescence - Heal: Level 40
(39) Numina's Convalescence - Heal/Recharge: Level 40
(39) Numina's Convalescence - +Regeneration/+Recovery: Level 40
(40) Miracle - Heal: Level 40
(42) Miracle - +Recovery: Level 40
(43) Regenerative Tissue - +Regeneration: Level 30
Level 2: Reconstruction
(A) Doctored Wounds - Heal/Endurance: Level 40
(7) Doctored Wounds - Heal/Recharge: Level 40
(7) Doctored Wounds - Heal/Endurance/Recharge: Level 40
(15) Doctored Wounds - Heal: Level 40
(15) Doctored Wounds - Recharge: Level 40
Level 4: Quick Recovery
(A) Endurance Modification IO: Level 50
(5) Endurance Modification IO: Level 50
(5) Endurance Modification IO: Level 50
Level 6: Hurdle
(A) Jumping IO: Level 50
Level 8: Divine Avalanche
(A) HamiO:Nucleolus Exposure
(9) HamiO:Nucleolus Exposure
(19) HamiO:Nucleolus Exposure
(23) Luck of the Gambler - Defense: Level 40
(37) Luck of the Gambler - Recharge Speed: Level 40
(37) HamiO:Membrane Exposure
Level 10: Maneuvers
(A) Luck of the Gambler - Recharge Speed: Level 40
(11) Luck of the Gambler - Defense/Endurance: Level 40
(13) HamiO:Cytoskeleton Exposure
(13) HamiO:Cytoskeleton Exposure
Level 12: Combat Jumping
(A) Luck of the Gambler - Recharge Speed: Level 40
(37) Kismet - Accuracy +6%: Level 30
(46) Luck of the Gambler - Defense/Endurance: Level 40
(50) Unbounded Leap - +Stealth: Level 50
Level 14: Super Jump
(A) HamiO:Microfilament Exposure
(45) HamiO:Microfilament Exposure
Level 16: Integration
(A) Doctored Wounds - Heal: Level 40
(17) Doctored Wounds - Heal/Endurance: Level 40
(17) Doctored Wounds - Endurance/Recharge: Level 40
(19) Doctored Wounds - Heal/Recharge: Level 40
(43) Doctored Wounds - Heal/Endurance/Recharge: Level 40
Level 18: Health
(A) Numina's Convalescence - Heal: Level 40
(36) Numina's Convalescence - Heal/Endurance: Level 40
(36) Numina's Convalescence - Heal/Recharge: Level 40
Level 20: Stamina
(A) Endurance Modification IO: Level 50
(21) Endurance Modification IO: Level 50
(21) Endurance Modification IO: Level 50
Level 22: Build Up
(A) HamiO:Membrane Exposure
(23) HamiO:Membrane Exposure
(43) HamiO:Membrane Exposure
Level 24: Dull Pain
(A) Numina's Convalescence - Heal: Level 40
(25) Numina's Convalescence - Heal/Recharge: Level 40
(25) Numina's Convalescence - Heal/Endurance/Recharge: Level 40
(34) Doctored Wounds - Heal/Recharge: Level 50
(40) Doctored Wounds - Recharge: Level 50
Level 26: Soaring Dragon
(A) Crushing Impact - Accuracy/Damage: Level 40
(27) Crushing Impact - Damage/Recharge: Level 40
(27) Crushing Impact - Accuracy/Damage/Recharge: Level 40
(31) Crushing Impact - Accuracy/Damage/Endurance: Level 40
(34) Crushing Impact - Damage/Endurance/Recharge: Level 40
(46) Accuracy IO: Level 50
Level 28: Instant Healing
(A) Numina's Convalescence - Heal: Level 40
(29) Numina's Convalescence - Heal/Recharge: Level 40
(29) Numina's Convalescence - Heal/Endurance/Recharge: Level 40
(39) Doctored Wounds - Recharge: Level 50
(40) Doctored Wounds - Heal/Recharge: Level 50
(40) Numina's Convalescence - Heal/Endurance: Level 40
Level 30: Hasten
(A) Recharge Reduction IO: Level 50
(31) Recharge Reduction IO: Level 50
(31) Recharge Reduction IO: Level 50
Level 32: Golden Dragonfly
(A) Scirocco's Dervish - Accuracy/Damage: Level 40
(33) Scirocco's Dervish - Accuracy/Recharge: Level 40
(33) Scirocco's Dervish - Accuracy/Damage/Endurance: Level 40
(33) Scirocco's Dervish - Damage/Recharge: Level 40
(34) HamiO:Nucleolus Exposure
(50) Recharge Reduction IO: Level 50
Level 35: Tactics
(A) HamiO:Cytoskeleton Exposure
(36) HamiO:Cytoskeleton Exposure
(46) HamiO:Cytoskeleton Exposure
Level 38: Super Speed
(A) HamiO:Microfilament Exposure
(45) HamiO:Microfilament Exposure
Level 41: Focused Accuracy
(A) HamiO:Cytoskeleton Exposure
(42) HamiO:Cytoskeleton Exposure
(42) HamiO:Cytoskeleton Exposure
Level 44: Calling the Wolf
(A) Taunt Duration IO: Level 50
(45) Taunt Duration IO: Level 50
Level 47: Resilience
(A) Aegis - Psionic/Status Resistance: Level 50
(40) Impervious Skin - Status Resistance: Level 30
Level 49: Vengeance
(A) Luck of the Gambler - Recharge Speed: Level 50
(50) Luck of the Gambler - Defense/Recharge: Level 50
------------
Level 1: Brawl
(A) Accuracy IO: Level 50
Level 1: Sprint
(A) Empty
Level 2: Rest
(A) Recharge Reduction IO: Level 50
Level 1: Critical Hit
------------
Set Bonus Totals:
+23% Enhancement(Accuracy)
+14% Enhancement(Heal)
+50% Enhancement(RechargeTime)
+117.5 (9.75%) HitPoints
+MezResist(Confused) (Mag 27.5%)
+MezResist(Held) (Mag 27.5%)
+MezResist(Immobilize) (Mag 31.9%)
+MezResist(Sleep) (Mag 27.5%)
+MezResist(Stun) (Mag 27.5%)
+MezResist(Terrorized) (Mag 36.3%)
+2.5% Recovery
+98% Regeneration
+2.52% Resistance(Fire)
+2.52% Resistance(Cold)
+3.13% Resistance(Negative)
+3% Resistance(Psionic)
| Copy & Paste this data chunk into Mids' Hero Designer to view the build |
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Something along the lines of 700% regen in there, give it a swizz if you have the cash, this is currently so far out of my league it's not even funny 
Ok I see your point Maelwys, i guess the best option would be to wait for i11 and check out willpower and dual blades. Thx Pipe for the build ill have a try, somehow i doubt ill be able to afford that unless i suddenly become obscenely rich 
The Title pretty much says it all i stopped using my scrapper but want to start using him again but have never been able to make him into a pvp build any help would be much appreciated