I had the same problem, as XBOX is currently not supported in my country of residence. The workaround I found was buying MS Points via Amazon.com. They have an option to purchase MS Points as an online code - ready to be redeemed either via marketplace or within the game itself. Hell, they even have them discounted by 1 dollar (1600MS points for $18.99). It will also cost you a bit less since Amazon.com does not apply extra taxes, which Marketplace seems to do.