They're called JIS screws (Japanese Industry Standard, I believe it stands for). You can find them on eBay if no hardware stores in your area carry them. If only I'd known that back in my early teens it would've saved hours of grief getting the screws off the cover of my XR75 to clean and change the points. A Phillips head screwdriver stripped them almost immediately.Les has done this before! :^)
people have posted the Phillips head screws have a Japanese standard pitch to the point, if you use a screwdriver from Sears or Lowes it will strip out the head. This is something worth googling, you can get the right screwdriver bits and have at least a decent chance of getting them off intact.
Or maybe its easier to strip them out and get new screws.