Hi, thehardtops themselves aren’t difficult to come by, it’s the mounting brackets that are like rocking horse sh*t!
At the front it’s just a couple of screws, it’s the brackets at the rear that are the problem, bmw stopped making them years ago & the z3 never had them fitted as standard.
Just keep an eye on eBay/z3roadster.org etc and save a big pile of money up
Rob