If you have a version of Sonar that had VC64 included (I think the last one was X2) try a custom/advanced install to see if you can install it separately.
If you have those old versions still installed it should still show up in you VSTs anyway. The only reason it would go away is if you uninstalled older version (or wiped your system and did not reinstall those older versions).
Be aware there is a reason VC64 was removed. It is a 32 bit plug that Cake removed because it was causing problems in the newer Sonar's. It should still work though but if your projects with VC64 start going f*cky on you that may be why.
It's a cool plug though. I think I'm gonna play with it on my current noodleturd adventure now that everyone has been reminding me about it.