For duty, I used a size 20 Uncle Mike's Pro3, I think that's what it's called. Triple retention, and I could adjust the thumbbreak down for cocked and safety carry.
For a belt slide, I use a Ross 17, made for the Glock 17. It's thumbbreak also lets me carry cocked and safetied.
It also fits the Blackhawk Serpa CQC for the Glock 21.
These are holsters I already had, so since they fit, I didn't bother to try and locate specific holsters. All of them work as though they are specific, meaning the fit is really good. As the Sar K2-45 is a CZ clone, it should fit in CZ 97 railed holsters. Also EAA Witness 45 railed holsters.