I may have missed something but pretty much all the bike screwdriver sets like the Park Tool one are Phillips, not JIS. There are JIS screwdrivers on eBay but usually from the USA with high postage charges. It seems a lot of money for one small screwdriver (for derailleur adjustment). Never thought to try a Japanese car dealership.
Mind you, it doesn't seem to make that much difference if you use a Phillips on a derailleur adjustment screw instead of JIS, if you're careful.