Re: Any way to get a copy of the paid version of C18?
Yes, MCC18 3.0 CD installs fine with Win7 PRO and the 3.46 upgrade does too.
However, when you've got hold on your CD, zip it down and put it in the code repository along with all the other tools you need to fix obsolete but active* software.
To be even better prepared for the future (not 100% guarantee) you'd make a virtual world where you set up the tool chain (and keeping the drive file safe). You'd be surprised, even 16-bit windows application can be fixed today if that would be of any interest...
* By active I mean software still in use by customer (even if any warranty, support asf. is out of date).