It’s happening. You catch yourself singing along to Britney Spears’s “Oops … I Did It Again,” and you know all the words. That “alternative” Moby album you bought last summer is now the soundtrack to a Nissan commercial. Suddenly you feel a powerful urge to broaden your musical horizons. Irwin Chusid, champion of nonconformists everywhere, whose recently published book Songs in the Key of Z: The Curious History of Outsider Music (A Cappella Books) chronicles the work of decidedly non-mainstream artists like the Legendary Stardust Cowboy, Eilert Pilarm (“the Elvis of Sweden”), and Shooby Taylor, the Human Horn, suggests a visit to See Hear (59 East 7th Street; 212-505-9781), a downstairs shop packed with homespun and obscure fanzines, comics, magazines, and books devoted to all types of music, pop culture, and counterculture. “The place is a farmer’s market for the First Amendment,” says Chusid. “Here’s where you find ‘hard-to-find.’ ” After browsing a selection of publications that includes Fresh Cow Pie, a music quarterly written by a “North Dakota tractor-driving farmer,” we’re inclined to agree.