Yup, they sure do, but hang on to your wallet because they ain't cheap, in fact, even on aegcartasia.com they still cost 73 quid, so taking postage into account, this is probably as good a place as any to get one, for 75 quid:
http://www.zerooneairsoft.com/product_info.php?products_id=2277
Takes 900 rounds apparently, but then again, I got five 160 round M4 mags which require no batteries or winding from aegcartasia for about 23 quid, so for the minor hassle of a quick mag change every 160 shots, I can easily carry 800 rounds with only four pouches, since one mag is in the gun, and that seems to me like a much more sensible solution to me money-wise, being literally less than a third of the price.