For airbrushing I use createx paints that are made for use in an airbrush. If I am hand painting I usually use apple barrel or one of those cheaper brands you can find in nearly any craft store or walmart. For sealing I only use Testor's Dullcote, it gives it a nice matte appearance and doesn't dry sticky or have I had any of mine yellow. As for the epoxy, I use Apoxie Sculpt from Aves Studio, I have yet to find it in any stores and as far as I know you can get it at the Aves website or there are some on ebay. Usually the 1lb container lasts me well over a year, but I don't do a ton of sculpting.
Hope that answers some of your questions!