On certain tools your arms are in different places, like with a sniper, your left arm is along the barrel of the gun not at your side, how would you do that on a gun, I have looked at free models to no prevail, i'm not necessary requesting a script but more asking where to start, maybe some Wiki pages, etc.
Maybe try the wiki's changing default character animations. I haven't really looked at it all that much. But I hope it can be of some use.