http://www.ebay.co.uk/itm/Elite-Force-Extreme-Precision-Airsoft-BBs-6mm-0-20g-0-25g-/171464967521?pt=UK_SportingGoods_Hunting_ShootingSports_ET&var=&hash=item27ec1bc561
agree with M_P - bought a big bag from LWA a while back, good .20's but not the be all & end all. Might try some .25's but think they are a few other good ones out there
http://www.landwarriorairsoft.com/batteries-bbs-gas-chronographs-c5/bb-ammunition-c61/elite-force-0-2g-bb-box-of-125000-p3135 & brill mags offer http://www.landwarriorairsoft.com/airsoft-magazines-c3/high-capacity-c51/dytac-300rds-bravo-magazine-for-m4-aeg-black-box-of-10-p3058
that is a lot of dough but if you get a few m8's to go in with ya that is some good cheap stuff that will see ya fine for ages