http://www.gamereproductions.com is a business that creates custom built NES, SNES, and Genesis cartridges using roms of games unreleased in the USA. They are completely functional on the original hardware, and from the look of some of the screenshots, look really professional. Some are actually less expensive than I'd expect for custom work, such as
Earthbound Zero which is only $29 including shipping. They also have
Sweet Home.
Also, for those in the area. The mall has a new shop called 3D Games that carries both old and new games and systems, including 3rd party controllers for old systems and new retro combination systems like the Retro Duo and the one that plays both NES and Genesis cartridges.