The screws need Hex Keys, hardware stores sell them. If you can't find hex head screws to replace them, just find other screws that fit.

But know that you know what they are called, your search should be a lot easier. Good luck, I've been looking at buying a gimble since my wife bought me a go pro. I only just edited my first video the other day and posted it on Dtube.
Nice work, sounds like you've been doing this for a few years now.