I can't offer the name of a lab that'll do this, but I can say that most photofinishers seem to have gone digital, so when you get "real film prints," you're really getting digital prints from scans made by the photofinisher, although many still use RA-4 paper and chemicals. Given that fact, you might consider processing the film yourself, scanning it, and sending the scans to somebody who'll make appropriately-proportioned prints on RA-4 paper. This would probably be safer than sending your film out, particularly to one of the big places; I have visions of an automatic machine slicing panoramic negatives down the middle. A smaller custom lab would probably be less likely to do this, but also more expensive.