I purchased my copy from a UK eBay seller in Yorkshire.
There's a place in Great Britain called 365 that also sells the game and will ship to North America:
SIMON UK/365 GAMES A couple people on the board here in the States have tried to order the game from Amazon UK, and it looks like their order went through, but the website says it does not ship computer games to North America, so the outcome of their orders is uncertain at this point.