I am desperately trying to find Flotilla on XBLA Europe. I had a look in all games under "F", and I looked for it with the search option but without any success. Any idea how I could get it anyway? Is it possible to buy XBLA games on CD? Or to get a US account just to buy a game and then switch back to my normal account?
You will have to create a new, American Live account. Create an American account with Hotmail or Live. I say create new because you won't be able to change your country if you already have a UK Hotmail account. I had the same issue, so I created a new account with "Location: US", used my credit card, and it worked. Any major credit card should work when purchasing points. If you can't use your credit card, you can always buy a points card from Amazon (or elsewhere) and redeem the card's code on your account.
The drawback here is that all the stuff you in your previous account needs to be re-bought and there is no way to transfer that ownership. However, the XBLA and other downloaded games should be accessible from the new account if you are using the same Xbox 360.