Another option is to look at the Dometic site for the replacement seal for a number of different model commodes. I would wager that the part number for the seal for a number of the non-VacuFlush models will be the same.
Not foolproof, but it may narrow your search some.
Current: 2020 Rockwood MiniLite 2205S
Past: 2018 Flagstaff MicroLite 21FBRS
Past: 2005 Flagstaff Classic 625D
TV: 2016 Ford F-150 3.5 EcoBoost