As for Microvision, the go-to emulator lately was MVEM, a fork of Paul Robson's emulator.
https://www.raphkoster.com/2017/05/07/microvision-emulator-release/

In MAME, external artwork with cartridge-based consoles is a bit annoying for the user, since at the moment there's no way to have per-cartridge artwork other than using -artpath.
eg. mame.exe microvsn somegame -artpath artwork/microvsn/somegame -nofilter -mouse