Do you have Chappell's Popular Music of Olden Times? A Dover reprint, first published around 1840 I believe. You probably already know a bunch of pre-1750 songs (secular) starting with Greensleves and The Fox and Barbara Allen and Matty Groves and Geordie. . . how long do you have to play for? The Burl ives Songbook (still in print, my edition is 35 cents) has the first chapter as pre-Revolutionary. Good Luck