Well the only place I've found jets is robbing them from other examples of the same carb, sort of a catch 22. Since you are running a modified car I'd suggest a different replacment TQ, they offer comparable performance and way better street manners. An early 70's version (post 71) will be the least expensive and jets&rods interchange freely with any other post 72 TQ, plus you get an automatic choke which can be nice on a driver, a later 70's Super-Quad version has an electric choke which is nice if you can't use a divorced choke with your current intake setup, they are on ebay pretty regularly for $100-$200.00. You could likely sell your current carb for as much or more even with a bad jet.