Dave in addition to comc.com and the ruthless beckett I use the following to search checklists.
https://www.sportscardchecklist.com/
https://www.hockeydb.com/
http://nslists.com/jachlist.htm
https://www.nhlhockeystickers.com/
also cardboardconnection is good.
Always looking for Blackhawk hockey, Notre Dame Football, White Sox and Bears Stuff. I have a plaque in my card room that says, "I could have been a millionaire but my mom threw out my baseball cards". How apropos!!! Collecting Chicago Blackhawks Hockey, Doug Wilson Hockey, Chicago Bears Older, Notre Dame Football in their college jerseys and Chicago White Sox.