Actually, if you have a US based credit Card and a US address that you use, you can shop at the US Amazon store. Since you are a US citizen, I think it is likely that you have both of these, perhaps using a family members address as the basis for a US Credit Card?
If I had to chose between the Sony and the Kobo, I would chose the Sony. I would ask a friend in the US to buy it for you though. It is a lot less expensive in the US then it is Europe even when paying the shipping.