I was interested in the question, so I looked up the shuttle and show accessibility; this is what I found:

According to this year’s website for the shuttle, it runs from Jan 30-Feb 16 and provides access to 43 show locations on four different routes. It’s set up so that if you park at one of the two “Shuttle/Parking Hubs,” you can pick up a handicapped-accessible shuttle (which, and this should be confirmed, will take you to any of the 43 shows). If you don’t need the accessible shuttle, you'd decide which of the 4 shuttle routes will take you where you want to go, then park at any downtown garage or “Shuttle/Parking Hub” served by the shuttle you want to take and, then, pick up the shuttle. Here's the shuttle link with maps showing routes, garages and hubs: https://www.tucsonaz.gov/park-tucson/gem-show-parking

There should be a master list of show locations accessible to the disabled, but I couldn't find it on the Internet. I can't imagine an event like this would be compliant with the Americans with Disabilities Act without it. I would encourage you to contact www.visittucson.org to ask about venue accessibility or the City of Tucson directly:
Office of Equal Opportunity Programs (they deal with accessibility)
City Hall
255 W. Alameda, 5th Floor
Tucson, AZ 85701
(520) 791-4593
Fax (520) 791-5140
TTD (520) 791-2639

Mailing Address:
Office of Equal Opportunity Programs /OEOP
P.O Box 27210
Tucson, AZ 85726-7210