What's the motor? And is that a ping-pong ball that you're using to hold a balloon tank?
I get my hardware from one of the web-order places (Micro Fasteners). I'm paying less than a dime a screw (I think it's less than a nickel), and now I have piles of screws instead of a drawer full of odds and ends, out of which I can always find three out of the four fasteners I need.