It should be available once the backlog of orders from Pebble's online store are shipped. It also depends if Best Buy wants to go ahead with it, depending on sales of original Pebble and the return rates for the device.
Personally, I also prefer getting it from Best Buy as you can drive to the store for replacements with issues.
In the interest of Pebble's overall success, availability at Best Buy would be a good move for both companies. On a personal level, I'm less excited about the idea for two reasons. First, as someone that pre-ordered, I would be EXTREMELY cheesed off if it became available in stores before mine arrived. Second, I used to work for Best Buy and have a strong distaste for the company and big box retail in general so whenever possible I order either directly from the manufacturer or through Amazon.