Best place to find a research kit?

I have farmed hundreds of zombies, searched tens and tens of silver/yellow crates and despite finding every blueprint numerous times i still cannot find a research kit. all i need it for is to research 556 ammo then i am happy. are they still even in the game?

Yes, its RNG. I found several research kits in under 20~ zombie kills. keep trying!

RNG?

Also black zombies or normal ones?

randomly generated number

random number generator

Raid someone

I found one in like, the first crate I raided :v: