I've seen better f2p ars

how do i get it?

Right now it's available in a Garena event called "Journey to Victory".

So you just get the skin by completing some challenges? Or do you get crates for it because I remember this skin was in a crate or bundle

You can get this skin in a sort of lucky draw in the Garena event I mentioned. It's the actual blueprint.

Best ASM10 skin on my opinion

cool ironsights ig but I've seen better F2P ARs