Clean the hell out of it. Use a bronze brush.Clean the chamber area with some IOSSO paste on a snug fitting patch. If that barrel is leaded-up and/or if there is a lead/carbon ring in the chamber's leade that could very well be your problem. Also, if you can get access to a borescope, you can check the bore or chamber for any damage. If the barrel was crowned at a loose spot, it'll never shoot well until/unless that barrel is slugged and cut at a tight spot in the bore and then re-crowned. If the chamber was badly cut/reamed, it'll never shoot well.
While I don't own a CZ, I own or have owned, over the years, rimfires, everything from my inexpensive store-branded Mossberg 346, Springfield 87A, 10/22, Rem 541, old model Browning T-Bolt, Cooper 57M and 3 custom benchrest rifles. Not one shot better real dirty. The most shots it has taken any of them to shoot well is 5-7 shots to coat/season the bore with the bullet's lube. IF a rifle does need to be real dirty to shoot well or needs more than a few shots to season a clean bore, that tells me that that bore is likely very rough.
