+1 on Bigfoot's comments above. I've been using a product called "Van's Instant Gun Blue" from C.S.VanGorden & Son in Bloomer, WI. Got it in a box of trade goods at a gun show, and it works pretty well, given careful prep. The look is improved with multiple coats, polishing lightly w/0000 steel wool in between. It will never be mistaken for original, but makes for a pretty good "experienced" look.

Larry