How can I collect new $1 coins? I don't want to pay $15 for four, though. I'd rather pay $1 for each coin.

I already have a Washington and an Adams, which I got as change for buying stamps at the Post Office vending machine. I don't need any more stamps, though. It seems nobody uses these coins as currency, at least in the Washington, DC area, where you'd think they'd be in wide circulation.