the company LImora, a specialist for oldtimerparts in Germany offers the softtop in a good lookinq quality, also with zip-off rear window. Looks very original in comparison with the softtop of my car. This would be my choice. Have a look at the site limora.com.
I got my last one from Rimmers when they said they were created using the original tooling via Tickford (IIRC). This is no longer mentioned, but Rimmers are worth considering.