Duggal in NYC has 11x14" hangers for their C-41 and E-6 dip and dunk lines (these are big machines that hold hundreds of gallons of liquid and take up a small room), but I don't know if they could handle 10x12", because it depends on having a hanger of the right size. The tanks are plenty big.
If you do enough of it, you might be able to work with a local lab that has a big dip and dunk and order custom frames for it, or if you can find a lab willing to process it in a Jobo, that could work as well.