The "Buffalo" is a great rifle for sure, almost bought one myself. You maybe able to buy an elevator sight which is almost the same thing but it will mount on the barrel about where your dovetail would be if you had one. You will probably have to have it drilled and tapped for a sight.
http://www.gun-parts.com/sights/

Try this webite and you can also try

www.midwayusa.com
www.brownells.com
I think, anyway you go you will have to have some gunsmithing work done.
Goodluck, thats a fine rifle.