SAN FRANCISCO -- Before dawn on a recent Sunday, Dan Oppermann stormed into a record fair, escorting an older Japanese man who had flown from Tokyo on a mission: to buy 5,000 records in one week. "It's getting tougher," said Mr. Oppermann, 65 years old, a retired government worker. "Everyone is really hustling, trying to find new connections, new sources."

Mr. Oppermann and a small network of fellow collectors host buying trips for Japan's record-shop owners, helping them find old LPs and CDs often considered passe in the U.S.-or simply bad-but that Japan's avid music fans have a yen for.

For decades, Japan's record shops have scoured the globe for records to feed the nation's collectors. Employees of Japanese retailer Disk Union once spent $20,000 in a day at Nashville's The Great Escape record store hunting for tunes including ones treasured by Japan's soft-rock and easy-listening fans. With U.S. record stores closing, this focus on obscure music is making supply difficult to find-and fueling secretive competition.

The U.S. has 1,700 independently owned recorded-music stores, about half as many as in 2003, according to research firm Almighty Music Marketing. The Internet has made music sellers and buyers savvier about prices, eroding dealers' profits. Vinyl is also back in vogue in the U.S., bringing new competitors.

Japan has surpassed the U.S. as the biggest seller of CDs, vinyl and cassette tapes, with 25.4% of global sales, according to the Recording Industry Association of Japan. Tower Records Japan Inc.-which survived its U.S. parent's closing in 2006-opens its 87th store this month.