Maybe MuLab Free does what you want.
If I remember correctly, VSTack for Mac was released later than the PC version. So, the first Mac version was already corresponding to the updated PC version. That’s why there are no Mac updates on the server.
Have a look at your Steinberg account. Maybe you have a registered serial number for your old Mac version. If so, you may try to ask for a download link or an installer CD.
Probably some Mac users could tell how the software was originally shipped (CD? Download file?), and how it was protected (CD? Serial number? Steinberg key?). I only know the history of the PC version: First, the installer CD itself worked as the copy protection unit. The update is a full installer that still accepts this same CD to “unlock” the program.