Here in Chile, the modelling stores sells only Enamels paints for modelling. They have also son water based paints (Vallejo), but only flat colors and for brush use, not airbrush.
Enamels dries slow, and sometimes it seems like never dries completely, because when you manipulate your models, it feels a little "sticky" and it dirties easily. Also, you can't make effects with oil paints above enamels.
On the other hand, lacquer (automotive) paints dries in few minutes, are very strong against frictions, and have UV protection. You can sand it if you find a dirt, etc. The best it's that you can go to an Automotive painting workshop and they can mix any color that you want, for a very cheap price (USD$5.00 for 1/16 galoon). I think that in USA or other big countries, this should be cheaper.