The only problem is that it only includes 11 leagues, seven of which are now included on OSC:
Cal Ripken League
Cape Cod League - OSC
Coastal Plain League - OSC
Florida Collegiate Summer League
Horizon Air Series
New England Collegiate Baseball League - OSC
Northwoods League - OSC
Prospect League - OSC
Texas Collegiate League - OSC
West Coast League - OSC
Can anyone else point out some other good sources of attendance information for any of the other teams or leagues?
Summer collegiate leagues are on the right side. Not sure how complete a list it is, and there are some leagues I've never heard of, but it's something.