I'm guessing you are using either the TC sawed flints or something similar with two pre cut angle surfaces. I'm pretty sure, with great care (eye/hand protection)a person could use a fixed grinder wheel to shave off one beveled edge thus allowing the new flat to slide closer to the lock flint screw and giving you plenty of frizzen clearance. This cannot be done with real black or yellow flints as they chip. Real flints come in all sizes and may be a better, safer, way to go for you. CVA mountain rifles use a small flint like a 5/8" size. TC flintlocks can use the pre sawed or 3/4" real flints. If you try to grind one edge, exterme caution and proper tools need to be utalized and you do so at some risk so this is not an endorsement of the above just something in my past was remembered. One more thought, a verticle fixed mount disk sander may also work. For those who will say this is too dangerous to try, most wood workers and metal fabricators have equal risks everyday using power tools and small objects and do it in a safe manner. The issue is safety.