Gotta ask it: Why would anyone make one??
209 primers are more expensive than caps, offer no real advantages over them in this sort of application that I can envision as far as ignition goes, and would have to involve a lot more than just a change of cylinder to be usable.
IMO, such an outfit would cost much more than most of the base revolvers out there and still need a considerable amount of skilled labor for installation.
When you can buy a cartridge conversion that requires only minor fitting for an 1860 from a couple of sources, why bother?
About anything can be had if you're willing to throw enough cash into the project. IIWY, I'd be sitting down when you get a quote for the job.
