Originally Posted by NessMcCool
Up 'till now the only one I've found are Difluoroethane.
Keep looking. Is mostly what I'd find early on (back before the propane adaptor was available, like in 2003 when I started airsoft) when looking in the stores such as Staples, Future Shop, Best Buy, etc. but I started looking in smaller computer stores and would tend to find the tetra there for the most part. Look into the electronics freeze spray as well, electronics supply stores.
Just checked out the 'Blow Off' brand duster sitting on the shelf at work, it's tetraflouroethane.