blanko00
I bought an ok quality airbrush, and just played with it, seeing what I could do. I also bought some frisk (a type of masking film). The airbrush was kind of entry level, but better than you'd use for model making. This gave me a chance to see where it could go, if it was for me and what it was capable of. Well that's how I'd start.

BassArtsCom
I looked for a long time localy and couldn't find any airbrush classes. I ended up ordering airbrush tutorial videos. I think it would be much more help than any class as they were more informative than any class I took in school. You also need to get an airbrush and just go at it. Videos and practice are the best. Take a look at my airbrush work.