MT Card...? I thought that the Gateway cards where the only ones to play 3DS roms and (hopefully soon) get multirom and so on.
There is the:
MT-Card
Gateway 3DS
3DSLink Card
R4i 3DS Deluxe
Orange-3DS
Edit: Check here Comparison of 3DS Flash Carts/Features (1/16/14)
Needs a small update but still good!