I have found a place with some older type 30 rd mags in stock here:
http://www.boomarms.com/sc/showcatalog9d8c.html?CategoryLevel=2&Cat1=Magazine &Cat2=&Cat3=&CategoryName=WA
They appear to have some newer type 33 rd mags as well.
Just FYI.
I've have had gear from BoomArms a few years back and they where fine to deal with then.
-Rob