I'd recommend a local shop in your area over a mail order outfit for only one reason...so you can go in and talk to them directly. I went into the local PPG dealer and asked a few simple questions and bought a gun and some paint according to their answers and recommendations. Each time I went in I bought something...even if I didn't really need it...like a roll of masking tape or some sandpaper. I figured they would eventually see me as a regular paying customer.
Pretty soon they warmed up to me and said, "If you ever have a question, just ask!" My plan worked! (I have lots of extra tape and sand paper, though!)
The best part about having a local guy is that you can take your mistakes to him and he can tell you what you did wrong. Been there...done that.
If you don't have any dealers nearby, you might cozy up to the folks in a body shop. They get their stuff from somewhere, and they could suggest some places for you to try.
Personally, I trade with Duncan Auto Paints in Olathe, KS. Good guys, there.