[celoknob]

Those numbers are provided in Bill James book "Whatever Happened to the Hall of Fame".

Between the years 1925 and 1933 between 50 and 55 HOFers played each year. The most was 55 in 1928. James also lists the % of total At Bats that were by Hall of Famers for each year. The most was a whopping 24% in 1929. Typically this number has been around 10% since WW2.

Edited to add: According to James there were 34 would be HOFers playing in 1921.