How can I access websites that blocks IPs that aren't from a given country?
It doesn't necessarily have to be free, as long as its secure and can't (easily) be sniffed (i.e. not those free php proxies but something reliable that won't be sniffed)
With TLS (SSL), a proxy server can't sniff the traffic. That's because user agents don't send along the HTTP request to the proxy server like they do for unencrypted HTTP. Instead, they use the
WARNING: a proxy server of any kind can still tell when and how often you attempt to contact which remote servers (by IP address) and can track roughly how much data gets exchanged in each direction. This isn't specific to proxy servers but is a general problem with encrypted traffic. Judge for yourself how much of a problem that is.
If you want to be more certain, you could always sign up for a cheap cloud service (linode, Rackspace, etc...) that gives you a virtual machine in a non-US datacentre. You get root access and you can run whatever proxy server or other software you want on that. The cloud provider can still sniff the traffic, but not as easily as if they were logged in to the server that runs the proxy server, and they probably don't gave much incentive to do so. Again, no guarantees: they ultimately have physical access to the server where your VM is hosted.
You could try Tunlr. Instead of using a proxy, or even a VPN, Tunlr is a DNS server that re-addresses some packets to make it seem as though they originate from a system in the US. As such, it does not intercept page data, cookies, etc.
It is mainly used for streaming video sites (Hulu, Netflix, etc.) and from what I can gather of how it works, I do not believe it would work with any arbitrary site by default, but you could always ask them to add (your) shopping site(s) to their support if it does not.
Caveat: Not surprisingly, using Tunlr (or any other workaround) to circumvent the geo-restriction is almost guaranteed to be a violation of the site’s terms of service with all the consequences that getting caught brings.