You want a small airbrush to finish models. I have been using my Thayer & Chandler Airbrush since the 1970s and I still use it for the fine detail. For an air supply, I recommend a CO2 bottle & regulator (you can get these at a beverage dispensor busines or go to a welding supply store and buy one. Thats were I get my gas refill too)
Here are a bunch of them and cheap
THAYER CHANDLER, Catalogs, Art Supplies items on eBay.com