Should've done a bit of homework on it if it were your first.
Mags are a huge problem for that gun in particular, and you can only get highcaps.
Did a google search and came up with quite a few results... These were all on the first page of results.
http://www.gunnerairsoft.com/online/...product_id=502
http://www.evike.com/products/31085/
http://www.airsoftmegastore.com/4132...-magazine.aspx