As far as I know I don't think they produced a particular production version of the Z3 MR/MC independent of BMW but had a development program of upgrades/accessories none which come cheap. If you did the AC Schnitzer alloy wheels, suspension upgrades, brake upgrade, exhaust upgrade, rear diffuser, spoilers, fog lights, door mirrors etc plus interior bits and pieces I reckon you could easily have spent £10 to15k on top of the cost of the car then there is fitting!! Must admit I haven't seen any AC Schnitzer modded Z3 MR/MC cars up for sale lately.
Dave Preston (Dave P) on the Z3 M Coupe Forum has the best range of AC Schnitzer gear on his car which he has managed to accumulate over the years. Really sets the car off.
Just to give you an idea of cost, there was a set of 4 genuine AC Schnitzer type 3 alloy wheels with tyres on the Forum going for £1200, now on eBay.
Link to AC Schnitzer site below:-
https://www.ac-schnitzer.de/en/bmw/z/z3-roadster-coup.html
There is a very limited selection of parts available from AC Schnitzer UK, most have of the ones I mentioned above have been discontinued.
Does that answer your query?