http://www.blendswap.com/blends/characters/boy-3/
http://www.blendswap.com/blends/characters/little-girl/
I'm not 100% sold on them but I'm going to keep looking

I kinda like this guy too, looks like he'd be fun to blast even though he's high poly it might work just fine!
http://www.blendswap.com/blends/charact ... -guy-v1-2/
Funny character:
http://www.blendswap.com/blends/characters/bge-2/
Haha we gotta make use of this somewhere:
http://www.blendswap.com/blends/animals/rubber-duck/
I think this could pass as a water gun, perhaps the sniper:
http://www.blendswap.com/blends/weapons ... nk-raygun/
Also chaingun, and an extra (for a waterthrower eventually?)
http://opengameart.org/content/steampunk-flamethrower
http://opengameart.org/content/steampunk-quad-shotgun
Another chaingun (obviously would need to have the bullets removed and maybe a watertank somewhere on it)
http://www.blendswap.com/blends/weapons/minigunn/