Actually, I also own a firing replica, in the "Sheriff's model" which I purchased from Cabela's. It has the shorter barrel and no conversion, but it is a high quality replica. I actually fired a few balls at the range and discovered that it is very accurate.
Cabela's offers a few different versions of this gun, like the one below, which is close to what you want. It is in .36 calibre and blued, not nickel.
There ya go. Just the thing ya need . . . git yurserlf a stainless steel conversion cylinder for it. Not the "hysterically coooo-rect" .36 . . . but able to shoot standard .45 cal. blanks. Grips like ya seen on the one in the "Autry Museum" can be had as well.
If you want to do your own conversion check out Kirst Cartridge Konverters at: http://www.kirstkonverter.com/default.asp. There isn't enough meat on the cylinder of a Colt Navy Model to convert it to .45 caliber. The Kirst Konverters are offered in .38 LC and they shoot fine with hollow base bullets.
I also have a custom converted Sheriff's model, however I believe it is "in the white" and not stainless steel.
If you want a custom, Bill Hickok set-up contact Jay Strite at: http://www.ravensroostcustom.com/27001/21501.html