I'm wanting to add a second crossbolt to my cz 550 stock and I'd like to have one that matches the existing crossbolt......is CZ USA the best place to get one, or are there better alternatives??

I bet you can call CZ and get one in a day or two. Now with that said, with my luck if I called they would be out.

Worst case change both out with Talley's or Bsquare from Midway or Brownells.....best I remember the factory crossbolts are about the same size, but I don't have a factory stock to compare for sure.