yeah but i cant figure out how to use mame core on retroarch. Seems that is it https://github.com/libretro/mame2003-libretro but retroarch uses dll for cores and there is not dll in that link. If someone knows something please post
It is a source repository - meaning, you must take a compiler and compile the code. Then you'll get your DLL (for Windows).
Alternatively, wait until it gets added to RetroArch Win32's updater service.