Attendance and winning percents, by team and by year, from various sources. The files are all in MSExcel format. So, use your "Save Target As" command to save them to your hard disk.
American Football League (AFL) I, 1926 (Winning Percents)
AFL II, 1936-37 (Attendance, Winning Percents)
AFL III, 1940-41 (Attendance, Winning Percents)
All-America Football Conference, 1946-49 (Attendance, Winning Percents, Team Prices)
AFL IV, 1960-69 (Attendance, Winning Percents, Team Prices, TV Rights Fees)
World Football League, 1974-75 (Attendance, Winning Percent, TV Rights Fees, Team Prices)
U.S. Football League, 1983-1985 (Attendance, Winning Percent, TV Rights Fee, Team Prices)