Man, what a bummer. I guess I've been really lucky because I have shipped tons of airgun stuff and only had some really minor handling issues.
Maybe try Mac1, I know at one time they were doing some work on the Korean guns, maybe they can hook you up. Those screws IIRC are like a pan head countersunk screw, kinda round on top, but countersunk. You might have some luck at Ace Hardware finding a match, but you'd have to bring the gun in to find a match, beware of gun fearing folk!