Chocolate – Food safe airbrushing

I've been hand painting colored cocoa butter into chocolates molds for a while now, but I'd like to try airbrushing the molds instead, since I've seen some impressive results. I can't figure out a food safe way to do this, though.

The most obvious way seems to be buying an oil-free compressor and a fancy air brush. That seems to be $200 and up, though, which is more than I'm interested in spending.

Another common approach is to use something like the Badget 250 and a can of compressed air. The Badget 250 is only around $15, making it a lot more viable. Apparently, even Norman Love does this:

"Another technique [Norman Love] showed us was airbrushing color into his molds. He uses "Mini Spray Gun Set 250-4" made by Badger company. It's the cheapest air brush out there. He hooked up to a can of air instead of a compressor. This cheap air brush lets you spray thick liquids (chocolate) and has easy clean up and no cloging. He mentioned plumpers use this type of brush… Oh, the can of air gets very cold while using and can freeze up. So he places it in a warm pot of h2o to prevent that from slowing him down. It also can be hooked up to a compressor, of course."

http://www.cheftalk.com/forum/thread/8093/chocolate-demo-by-norman-love

That's great, except that all the compressed air I can find contains a propellant which is highly unlikely to be food safe. Can you buy food safe compressed air? If not, how do you do food-safe airbrushing without spending hundreds of dollars?

Thanks!