Apple's (NASDAQ:

) long-awaited

has been selling so fast that the company is no longer shipping them to retailers. That is according to Mac expert Justin Block, who (during a recent shipping inquiry) said that if consumers want to buy the Next-Gen MacBook with Retina Display, they are going to have to

. Block said that Apple has been unable to keep up with demand, as sales of the new MacBook have far surpassed the company's expectations.