All users who have been trying to purchase a standalone Magic Mouse ended up with the same conclusion, there is none available. The only chance to get one would be to order it directly from the online Apple Store. Other distribution channels never received any units to be sold. According to several sources and reports, things should no improve over the coming weeks. In New York, it is not possible to get one in any of the Apple Retail Store, even the online Store is now indicating a 7 to 10 days delay for shipping the Magic Mouse. Apple can not get enough units produced to be sold as single product, and most likely keep its stocks for feeding the production of iMac as the Magic Mouse is part of the package. So, this could be the sign that Apple is selling iMac at a higher than expected level.
