MOST airsoft guns are not even slightly operating like real guns. They are RC cars, shaped like guns. Literally, RC car motors drive gears to push a piston of air to make the pellets go poof out the barrel. Batteries to drive them. Nothing remotely gun like. You couldn't get a cartridge in there much less ignite it.
A decent number work more like a real gun, in that the bolt/carrier or slide reciprocates. These still are miles from a real gun in operation. The hammer strikes the back of the magazine to release a puff of pressurized gas, etc. etc. Again, no place for a cartridge to go (a straight 6.000 mm tube, no chamber), no way to ignite it, and even on the increasing number of mostly/all metal guns, it's not good metal, they would explode on the very first shot.
A very, very small number 30 years ago (relative to the mass of them out now now) fired cartridges, either plastic pellet holders, or a tiny number actual primer-activated things. Even those were ATF inspected, approved, Not A Gun, not easily converted to a gun.
By the time you get it converted, you'd be better off making something from scratch you did so much work.
The closest that ever happened was BB guns and aside from general gunfear that airsoft look like guns, MAYBE this is where it comes from? A few east block BB guns were/are built off real gun frames/receivers, made in the actual gun factories. Two I know of are the Baikal mp-654k (Makarov) and the Junkers AKM, made in the Kalishnakov factory. I have seen a couple reliable sources that these have most of the parts, good metallurgy, etc. so can be converted to real guns but it is still a lot of work. Pretty easy for an AK maker in the US to do, but in a no-guns country, you are already not going to have those parts/skill. Or... you could make your own guns pretty easily. You are not far from laser cutting a receiver flat and proceeding from there at this point.