I've also just had this problem. I've emailed Vuescan and they replied rather quickly to tell me they have no plans to support this hardware.
I work from home as a freelance artist and I use my scanner daily. The fact that it isn't supported in OS Catalina is actually a nightmare.
the next comparable scanner I can find at this size is this one:
https://www.amazon.com/Plustek-Flatbed-Scanner-1180-Blueprints/dp/B01MZXE0OV/ref=sr_1_1_sspa?crid=308C2UKN6LPFW&keywords=11x17+flatbed+scanner&qid=1573851764&s=electronics&sprefix=%2Celectronics%2C168&sr=1-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyMVY0RFlTRjFPQ1JIJmVuY3J5cHRlZElkPUEwOTk1MzQ0M0dLMVU0UE9ZWUFFQiZlbmNyeXB0ZWRBZElkPUEwMDc3NjYzMUZVRlo3WTBHTEtNRCZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=
