Check out this Gameboy cartridge breakout PCB by Driptronics on Tindie:

Cartridge Breakout Board for Gameboy

A Gameboy cartridge breakout PCB that gives you access to a Gameboy cartridge’s connections.

Works with all OG cartridge formats (GB, GBC & GBA).

Clean, simple, and cool.

Comes with 2 x 16 point male Dupont headers for you to solder yourself.