Only aftermarket mags I would even think about buying is MecGar - they actually make the mags for many manufacturers. Other than that - they are all junk - with Ramline being the absolute worst.
I don't know if Mecgar makes CZ mags - U can probably check sites like Midway USA and Brownells and see. Otherwise, get your local shop to order U some factory mags. They will cost more - but as U see - aftermarket mags generally suck, unless it is for a 1911.