I'd guess they'd maybe be more under broadsides, but people seem to list them as posters.
I've seen reproductions like (mostly ebay links, not my items):
1903
1919 Game 3
1919 Game 4
Heritage sold 1955 Game 1 autographed repro
And this
1932 Game 1 looks possibly real.
I've looked around some of the bigger auction houses' past sales, and can't really find anything like them.
Are those reproductions actually based on existing authentic examples? If so, have the originals ever sold anywhere?
Or, are they all fan designed/later reproductions?
I just find it a little hard to believe that they'd be so stylistically similar spanning 50 years... not to mention seemingly being of some of the more relevant World Series.