Go to Walmart, Gamestop, Toys R Us, or any other store like that.
I'll post a link of what you'll be looking for:
Video Games - Wal-mart
Go to the bottom right picture, that's what you need (
Sony Memory Card Adapter PS3).
I too was disappointed to find out that the PS3 didn't come with a memory card reader, but I got past it.
Oh, and it's very easy to use. You use your USB cord and plug it into the Memory Card Reader, then put your card into it. The copy the information onto your hard drive, and then it's all over.