Generally speaking, EAA Witness mags for the small-frame Witness/Clones will work in CZ 75Bs. (The .45 mags are virtually identical.)
CZ's mag release is set just a hair higher in the grip than Witness mag releases, and as a result, Witness mags won't work right without modification.
(When this happens, they will sometimes not lock in place, or if in place, will press up so firmly against the underside of the slide, the slide won't move properly. You can fix this with a dremel or small file, by enlarging the top of the mag release notch to let the mag drop down just a bit.)
The plus: .40 mags will generally work with 9mm rounds, so you can get some cheap semi-hi-caps.
Baby Eagle mags will work too, and they're often available cheaply. (Same possible problems.)
CZ factory mags are now available from a number of sources, and they're very reasonable. Unless you're getting the "clone" mags for about $7 or $8, I'd stick with factory or Mec-Gar mags.