The aerial section lists a few more films.

I figured the 6x12 back would be for 4x5 -) Plenty of plain 70mm backs for graflok back cameras. But they mostly seem to be 6x7. I have something stuck in my memory about Linhof making a 6x9. If you really want 6x12 from 70mm then the likely option is to find a back you can modify.