Old Cardboard has created a tool that is long overdue. They have just put up their Baseball rookie card database that includes the 5 earliest cards of every Hall of Famer. Not only does this include the Topps or Bowman rookie cards, but also includes earliest examples of players on minor league cards, obscure regional issues, limited edition photo sets and other strange collectible sets. In a sense they are showing a players true rookie collectible. Check it out here.
For instance, Walter Alston's first true card came out in 1952 in the Parkhurst set featuring primarily Canadian Minor Leaguers. Parkhurst is famous for making hockey card sets.
Don Drysdale's first true card/collectible was a team issued photo from 1956.
Tommy's first card is a minor league issue from World Wide Gum called 1950 Big League Stars. The set features only players from the International League. I find it funny how they spelled his name back then.