Extreme rarities listed on eBay
 

https://www.ebay.com/sch/i.html?sid=...6.m3561.l49496

1919-21 Barker Bread Joe Garrity
1929 Leader Novelty Rogers Hornsby
1936 Kroger Bread Johnny Riddle
1948 Remar Bread Oakland Oaks

I believe each of these is either the only known copy of the card or one of 2-3 total examples.