You can get custom resonator sizes, or another method is to just not order resonators on pads under about 22mm. Save a couple of $$ (or spend that money on some teflon or other cool stuff at Music Medic). I'm not sure that a tiny resonator does anything for you that a slightly smaller rivet wouldn't do.
Worst case scenario is that, on a tone hole like C2, even a little resonator might be large enough to cause problems when you float the pad. As you pull out the old pads, take a good look at the old impression ring. Sometimes it is not in the center of the key cup and adjusting the key cup is not possible. In these situations, you have to be careful if you're trying to put in large resonators. The "standard size "resonator for that pad may actually be smaller than the tone hole, but because the pad sits off-center, and the resonator creates a depression ring around it, the 'standard size" resonator for that pad will cause sealing problems. Better too small (or nothing at all) than too large.
Black with silver rivetless domes on a silver horn (like my CMel) is my favorite combo.
Mark