We used to do all kinds of coatings at blackdog. We even thermal barriered(sp) a couple scca track cars in the exhaust ports and couldn't tell. Just looked like carbon and smoothed the casting. Porting was not allowed so we coated it smooth. We also teflon coated piston skirts and cermic coated piston tops(excellent for turbos). Products can be bought online from lots of places. What are you coating? Parts need baked after coating so small parts went in a toaster oven.
Most coatings are applied with a small air brush.

coating info
googled