I imagine you could strip them down and nickel them yourself using a Casswell (sp?) electroless nickel kit. The smallest kit is well under $100 and will easily do two revolvers. On a revolver such as that the nickel would come out with a slightly 'orange peel' look to it, i.e. slightly 'bumpy' ....but that would just make it look more authentic, IMHO.
The bone case color hardening involves encasing the pieces in bone charcoal, heating them to cherry red, then quenching the works in water. I would hesitate to try it myself on a real Colt, but on a cheaper revolver I wouldn't lose too much sleep over it if I ruined it in the process
Who knows ...a 'homemade' bone case color hardening job on such a revolver with a rough finish may turn out looking pretty cool...and 'authentic' for a 100+ year old revolver.
I'm getting ready to experiment with bone case color hardening right now ...I'm waiting for the clay box (which will contain everything during the heating/quenching process) to dry so I can bisque fire it. I was also thinking that one could probably forego the clay 'wrap' and wrap the works up in a heat treating foil....which is something I'll have to look in to.
Another idea would be to wrap the works up in Playboy photos (potters use Playboy photos to wrap raku pottery as the colors in the ink transfer to the pottery during firing) and then dip the works in a high fire clay such as Satanite. That might also turn out pretty cool looking ...a bone charcoal/Playboy ink case color hardening