One of our favorite WDW pages reported that Magicbands may now be purchased from certain non Disney businesses, including the Swan and Dolphin resort hotels over in the Epcot and Disney Boardwalk areas of WDW.
(Although on Disney property, the Swan & Dolphin are operated by an independent business).

In addition, Magicbands are also being sold by independent hotels in the Downtown Disney Springs area of Orlando, as well as at the Character Warehouse at the Premium Outlets Mall along with certain outlets inside airport malls.

No word has been released yet about Magicbands going on sale at official Disney Ticket Centre partners, but that could be expected as a possibility in the future as Disney work hard to ensure that as many guests as possible adopt the new Magicband system for their vacations.