Is Apple about to replace its Apple TV with a new model? Apple's set-top box is running out of stock in multiple stores, which could signal that Apple is about to replace it with Apple TV 3.1.

Tech site 9 to 5 Mac reported that the current Apple TV is already listed as "unavailable" at U.S. retailer Best Buy. According to sources inside Best Buy, the retailer has been unable to order an Apple TV from their product ordering system as it is listed as "currently unavailable".

It should be pointed out that Apple traditionally lets stock run down before the launch of a new product. And Best Buy online isn't the only retailer having trouble finding Apple TV stock. Amazon, Target, Buy.com, and Radio Shack all list Apple TV as out of stock or taking weeks to ship. Walmart has completely removed the device from its online store. International retailers in the UK and Germany also show no supplies or small numbers of Apple TV. Apple's Australian online store does show the device in stock.

In the U.S. a new model for the Apple TV has been referenced in the iOS 5.1 beta software. The next generation Apple TV is codenamed J33 and Apple TV 3.1 in the iOS 5.1 beta software. It is possible that Apple will announce the new Apple TV at its March event which is expected to launch the new iPad 3 or an upgraded iPad 2.

It's not exactly clear what specifications a new Apple TV will have aside from Bluetooth 4.0 as mentioned in the iOS 5.1 beta. Users are hoping for full HD support as the current model is limited to 720p support. The next generation Apple TV could also have full iOS app support with Siri voice control feature to really set it apart from Google TV.