If you go to the timber framers guild home web page and click on Resource Guide and enter the subject of CAD software you'll get a list with several companies that sell them.
Also, the timber framers guild conference this November is have a pre-conference event and two different companies are offering a 3 day workshop to learn how to use their software. You can check that out on the home page under upcoming events, under eastern conference, under workshops. Good luck with your project. Jim