alpha-usb.com is one of the best sources in USA. First of all they sell brand new chips, unlike the ones that you can get on eBay. And they are wholesalers, so their price is very reasonable. I'm a photographer and this company is my vendor.
I have been with Alpha-USB.com for two years now. Placed 5 orders, the latest was on Feb 21st and product is already in my hands. Everything is perfect, good price and exceptional service. Highly recommended vendor!