I am sure that Ruger will only sell one IF they install it, so you would have to ship it back to them. Your first model Vaquero will take cylinders from the N.M. Blackhawks ( 2 screw, don't know about the newest smaller framed ones ), so it should not be difficult to find one. If no one here can help, keep an eye on on-line firearms auction sites, pistol parts ( yeah, I know it's a revolver, but the one site I watch lists "pistol parts". THEN, hopefully, once you find one, it will fit your frame properly.
Mark