Apple’s stock of AirPort base stations is beginning to sell out, MacRumors reports, following the company’s formal exit from the Wi-FI router business last month. MacRumors notes that the AirPort Extreme is already being listed as “sold out” on Apple’s online store in the U.S., although it remains available in limited quantities in other countries, such as Australia, Canada, Japan, and Singapore. The smaller AirPort Express…