Afaik, there isn't...but what you can do is below:
Lifted from Paragonwiki
/target_custom_next parameters
Cycles through matching targets in near to far order
Parameters
enemy - Hostile enemies
friend - Friendlies (including pets)
defeated - 0 HP targets
alive - Living targets
mypet - Inlcude only your pets
notmypet - Exclude your pets
base - Include only passive base items
notbase - Exlude passive base items
teammate - Include only teammates
notteammate - Exclude teammates
Everything else will match the name of the entity
Well, you could technically make a bind that would contain all the boss names in the game, but other than that, no.
Dunno if its any use but just in case, I was after something similar and started using this:
/bind control+] "beginchat /bind 1 "targetcustomnext alive XXX""
The same as you've already got but its dead easy to change what you're after by replacing the X's
Kneeling girls! Statues driving cars! What's going on? Ten years ago a man was arrested in the area for driving statues around in a car. Was it him?
@Ted Maul - The Echelon
Is there a bind for finding bosses.
For example I know
/bind b "Target_name lead"
will find lead bricks, lead shockers etc, but is there one that'll find any bosses?