Global supplies of Apple’s MacBook Air laptops are dwindling as the consumer electronics giant prepares to refresh the line, 9to5 Mac reports. The Apple enthusiast blog cites multiple sources in stating that shipments of the Air are currently constrained, and the site also points out that remaining MacBook Air inventory is now on sale at several retailers. Apple’s online store is currently offering refurbished models at an all-time low price of $829, and Best buy has brand new models on sale starting at $938.99 for the 11-inch version. Earlier rumors suggest Apple plans to issue an incremental update to its MacBook Air line later this summer, likely featuring Intel’s new Sandy Bridge processors and Thunderbolt I/O ports.