happycat,
I did an internship with an exhibit company a few years ago. Although I wasn’t really responsible for doing any of the 3D modelling, I believe the person who was responsible used FORM-Z.
Also, I am very sure that Interior Designers and Architects use AUTOCAD in their practices.
Try searching some Coroflot job postings that are hiring Exhibit Designers. This should give you an idea on the skills you need and software that the companies require you to know. Plus, it gives you a list of the many different exhibit design companies out there that you could apply to when searching for work.
Enjoy!