Milsim Labs

I just had to.

Milsim Labs specializes in the creation of foam ordnance for milsim purposes. Here are some examples of products they turn out:

40mm grenades designed to be used with 

paintball/airsoft 40mm launchers.

A cheap cap-firing booby trap.

Foam folding training knife, great for 

self defence/martial arts instruction.

I don't personally own any of their products yet, but I hear good things, and might try picking up/reviewing some of their 40mm rounds.