The internet is the best place to find hard to find plants. Many nurseries will deliever plants to your door step. This will probably be your best bet, it wouldnt hurt to call around your local nurseries to see if they may carry them.
You can go online and search for companies that carry them I am not sure if they sell them in local stores or not but you can find them online and there are at least two companies within the states that I know for sure that sell them and they will even tell you when and where to plant them.
You have several options for buying your blue moon rose bush in the US. Try searching the internet for online dealers or contact your local florist or nursery.
A number of florists and gardening shops in the United States might sell these rose bushes, as do a number of online sites, so be sure to look through your phone book and search around on the Web.