I buy direct from the manufacturer whenever I can.
The prices outside of Amazon will be higher though, that's the reason for this enforcement, the "Amazon tax". Cory Doctorow has been talking about it for a while. I'm glad to see someone that can do something heard it.
Finding stuff outside of Amazon isn't easy, though. Search engines barely show results for anyone outside Amazon, Walmart, and ebay. Too often I'll find a retailer for a while only for Amazon to buy it later or otherwise destroy them (I miss Woot and Jet and Fictionwise and Bookpool, &c).
Always worked well enough for me.