They happen fairly often, and are usually impromptu "Hey everyone, I'm forming a raid, come on down..... pylons are dropping... pylons are down... *everyone shows up finally*" kind of deals.
Haha. Ah. Okay. Good to know.
I'll make sure and just stick around in RWZ later in the day. I'll probably get my stuff in a snap. 
RAWR.
:3
Member of Operation Unlimited Justice!
You only wish you were this epic.
10 Drop Ships taken down.
I think there are global channels you could join that would help you with some hints as to when these are happening.
Char Site | My DeviantArt
Global=@Thornster
Basically are there any weekly type Ship raids going on?
I'd love to know so I can get all of my Vanguard Stuffs.
Thanks!
RAWR.
:3
Member of Operation Unlimited Justice!
You only wish you were this epic.
10 Drop Ships taken down.