We sell these occasionally at the company I work for but we don't stock them. I would try Grainger, Walter A. Wood, or Northern Tool. Are you using the respirator for spraying Gel Coat? If so be sure that you get a real good one. They are not cheap! Make sure the cartridge is rated for the chemical you are spraying! You might even need a fresh air hookup. Also make sure that you don't have any flames or sparks (compressor switches/relays or water heater pilots in a garage) around while spraying. You probably already know all of this but I used to work for a company that handled this type equipment and you would be surprised at some of the things people would do when using resins and paints.