Even though international customers login to Amazon's US store using a
user@amazon.com ID, it's true that not all Kindle books, magazine subscriptions, etc. are available internationally, which reduces the availablility of materials to non-US Kindle owners. This is more than likely due to publishing rights, etc.
There was a vanilla mastercard/gift certificate
hack floating around, plus there's the usual US Credit Card, US address, and US-based proxy trick - just search for these on Google. The bonus is that you can also avoid the $2 transfer surcharge. You won't be able to transfer the books wirelessly, since the US account won't know about your international Kindle.