I do not believe you can just replace the blade on the rear sight. The tritiums are in little tubes that is much longer than the thickness of the blade. I have seen special Bomar adjustables on Les Baer's pistols that have the tritium inserts, so you might check if Bomar make them to fit the Kimber cut. Also Heinie has a new FIXED rear replacement for the Kimber that can be had in the Straight Eight configuration.