Apple Insider reports that third-party resellers are now starting to see limited availability of Apple's big-screen 27-inch desktop Mac

The lack of availability at Best Buy is particularly noteworthy as the retailer's website simply states the all-in-one computer is "not available" both online and in store, with no indication of a restock. In contrast, Apple's newly released MacBook Pro with Retina display is advertised as "backordered," with new orders expected to ship between 7 and 30 days from Best Buy.

Limited availability at Mac resellers is often one of the first signs that Apple is drawing down inventory ahead of a product update. And the iMac line is due for an update, with the most recent refresh released over a year ago, in early May of 2011.

  Supply of Apple's 27" iMac drying up as Ivy Bridge upgrade awaits