Dave,
I've used GunKote to refinish firearms. It's really good, but requires a cure in the oven. CeraKote is similar, but I haven't used it. I believe CeraKote has a non-baked version, but I'm still doing a little research. Any metal-friendly paint should work, given the exteriors just don't get hot, but I like the finishes offered by those I mentioned, as well as the fact they are pretty much impervious to solvents, so cleaning should be a snap! I'm thinking a desert camo pattern would be pretty cool!