Been awhile and wanted to update this thread---with a great deal of help--much of it from the BBM Sumo Card Collectors Facebook group, I was finally able to complete all of the BBM Modern Sumo sets from 1997 forward. If you have an interest in finding/trading/buying Sumo cards, this would be a great place to start:
https://www.facebook.com/groups/1630250003925942/