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You can find compressed air cans at office supply stores, electronics stores, and online suppliers. Test it by aiming it downward and pressing the nozzle down. Get a feel for how much air comes out with each spray. Purchase a can with a straw for increased accuracy. Screw the thin straw onto the nozzle of your compressed air can. Give it a test by aiming it downward and pressing the nozzle down. The air should blow from the tip of the straw.  Tighten the straw if you can feel air coming out of the sides of the nozzle as you spray. Skip the straw if you're comfortable aiming your compressed air can without it.
Purchase a can of compressed air. Connect the straw to the nozzle of the can to improve accuracy.