Please add it in the next version of HBMAME.

mslug3b6 Slug summoned version.

Hello tnswns thank you very much for your contribution, this roms is already included in HBMAME:
You can locate it with this name in the emulator:

mslug3rma35: Metal Slug 3 (Enemy Soldier Reset Prototype Store Version 2018-07-21)(Revised Version Cannon Mix 2.1 [2019-12-03]

ms6s08: Metal Slug 6 (Enemies Resetting Version + Summon Mount Edition 2019-07-20)