OK after experimenting with R4 carts using my old NDS I decided to take a leap and purchase a Gateway 3DS two-cart package.
My current OFW for my 3DS is 9.2.0.19 so I don't think I have to downgrade, but following the instructions on the Gateway 3DS guide I have encountered two problems...
they need to have a strong line up on the launch titles too. I think they should move metroid prime 4 to the next console because by now it has been quite a while and there's no release date scheduled yet