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