The closest thing to a Flash Bang Grenade that can be used for Airsoft games can be ordered from  £1.65 according to its maker, Enola Gaye... "The Flash Grenade has been developed for Airsoft and Paintball players whos game play is in low light, urban, CQB etc.. It delivers a low bang and white flash that confuses your opponent allowing you time to enter the room and dispose of you newly confused foe. Unlike the MK5 Thunderflash, the noise report of the Flash Grenade is much lower in pitch and overall volume. Designed with a friction ignition, all you have to do is pull of the cap and strike it across the fuse head.

The product effect from a flash grenade is from the base of the tube, so unlike the MK5 the tube is not destroyed upon ignition."