If the tool has a long enough shank, just grind your own flat on it. I do this to carbide endmills when needed. The flat doesn't need to be nearly as large or as deep as they generally are supplied. I have a 3/4" carbide endmill that I regularly run at 130% spindle load on a 20hp Haas that has a flat that's probably only 1/16" deep, if that. It aint pretty either, but it sure works well.