Unfortunately we don't have a Mac version to offer as this would require a near rewrite of our code and having to reverse-engineer the Mac binary. Process injection is also less reliable on Mac than on Windows. We don't expect to have one in the future.
If you bought the Mac version of the game on Steam, you could use Boot Camp or Parallels to boot into Windows and install Vice City and VC:MP there with the Steam version. If you bought it on the Mac App Store, we can't really do anything.