Walgreens sells a Universal USB kit which includes a USB host adaptor. It's around $10-12. I also picked up a similar kit at Big Lots that included the adaptor.
They aren't labeled USB host adaptor, but instead mini-A (or is it B?). Anyway, if you plug it in, and type 'dmesg', if it's the USB host adaptor, you will see messages saying that it detected a new USB hub.