@rasp_renegade hello. As with ColecoVision and Intellivision...all emulators....Google is your friend for any BIOS/ROM files. And also keep in mind, there are variations to some that you have to keep trying versions until you get the right one.
@nightbirdmedia mupen64plus-gliden64 isn't a libretro emulator so you can't use the retroarch menu. The save states are not compatible but there are conversion tools out there if you have existing save files. The default save file location for standalone mupen64plus is a little weird but you can change it by editing your mupen64plus.cfg and pointing it to save to the rom folder.