Cooler Master would be a logical choice, if you are missing parts they should be obligated to supply them.
But if you can specify what you mean by H screw, then you may just be able to buy the appropriate screw from any hardware store. Not like they use anything super proprietary.
If you mean from the manual, labeled as H, I'm afraid the line drawings aren't enough to get a thread. But considering all they do is keep the bracket on the cooler, any screw with the appropriate thread should do. Take the cooler into a hardware store and try some machine screws. My guess would be M3 or M4.