I use a supplied air respirator. Hardeners (isos) are bad for you. A good respirator that fits correctly supposedly works better than nothing, but I have a beard. There are some good supplied air respirators for about 400 dollars. The payback is not having to buy the expensive organic cartridges (also your lungs will pay you back). Great for sandblasting also. The nice supply of cool air is refreshing and easier to breath as you don't have to pull your air through the filter.
The brand I have is Hobbyair. It is identical to one that cost almost twice as much, but doesn't carry the NIOSH certification you would have to have if you worked in a "buisness".
Check out some of the industrial coatings from some of the major paint companies (ppg, dupont, etc.) They arent cheap but no where near the price of automotive paints. They can mix your colors, tough as nails, covers well, and takes the weather much better. You would need the paint, hardner, maybe an accelerator, and the correct thinner. Proabably $150 bucks for a gallon, but it would paint an entire tractor easily. As much work that goes into paint prep, it is not that much more for a job that will last.
