Ephraim, the Whitney replicas are .36 caliber, but the Ruger Old Army leans more to the Ruger Blackhawk design since that is its "parent" than to the Whitney .36 caliber.
Its actually hard to call the Ruger Old Army (or "Navy") a "replica" revolver.
The Whitney .36 caliber revolver leans closer, with its octagon barrel to the Remington .36 caliber belt revolver, even with its shorter barrel. Again, IMHO.
I think "commonly found" should be emphasized here. I admitted to the possession of a Ruger .36 caliber revolver to get Crawdad's attention (it worked), but due to less than 50 out there, it would not be a candidate for the original poster.
The Muzzleloading Forum at
www.muzzleloadingforum.com had a Whitney .36 caliber replica Revolver for sale just a few weeks ago and it sold for $400.
Crawdad1, yes it is a custom-worked Ruger Old Army. It is fitted with a brand new round or octagon (I think mine has a six-sided barrel) 9mm caliber barrel fitted with a patridge front sight and a Bo-Mar adjustable rear sight. The cylinder chambers are sleeved with stainless steel tubes. Everything else is standard Ruger Old Army parts.
I'm guessing maybe less than 50 were converted to .36 caliber by competent gunsmiths known only among national-level shooters. Respected by both N-SSA & NMLRA revolver competitors back in the '80's and '90's, Tom "Mulie" Ball was the "Go-To" guy. Others were produced by Dick Bauer & Tri-L gunmaker, Rob Lewis.
Their use would have been seen only at Friendship (IN) at the National Matches, and may have appeared at various State Shoots around the country.
You might see one show up on Gunbroker in your lifetime. Usually, they are sold to fellow competitors at the national matches. I bought mine from the 1997 National Muzzle Loading Pistol Champion, a friend of mine, who I shot against from 1986 to 1999 at Friendship.
I'll post my Ruger "Old Navy"
and customized Ruger Old Army "Dragoon Model"
(my name for it) .44 caliber on the Ruger Club page soon.