Claris hasn't updated Claris CAD for 21 years, and changed their name to Filemaker Inc. in 1998. I heard rumor that they abruptly dropped the product over some sort of patent dispute, but I can't find any hard data to confirm that.
I have searched for an OS X 10.8 compatible application that will directly open Claris CAD documents, with no luck so far. Searching these and other forums, I have heard about some obsolete versions of other programs that are capable of opening Claris CAD documents and saving the file in a more modern format. That's the best I've found so far. Sorry I am not being very helpful but I'm in the same boat.
Another possibility is to continue running Claris CAD, using software that emulates the Mac OS 9 world. One I keep hearing about is SheepShaver, but I haven't figured out how to make it work yet. Apple's official answer was the "Classic" environment http://en.wikipedia.org/wiki/Classic_Environment however the last OS to OFFICIALLY support that is 10.4 Tiger, and that will not install on too new a machine. http://www.everymac.com/mac-answers/mac-os-9-classic-support-faq/last-macs-to-su pport-macos-9-classic.html
I honestly think there's a market for Claris CAD today. A LOT of people still make mechanical drawings and it can't be beat for that. Also a lot of CNC work is genuinely 2-D. 3-D is very confusing and leads to mistakes.
I also think Apple should go the extra mile to ASSURE that every Mac app ever written (properly) should run on every Mac ever made now or in the future, either by not dumping things like Classic, or by supporting third party efforts. But that's just me.