I had previously never seen them before. I actually picked it up at a bar. I was even at Goose Island last month at the brewpub in Clyborne and was laughed at when I asked if they had any. Hopefully it will get easier to find. That and Founders KBS have been my unicorns so far.
It sells out pretty fast, though New York is supposedly swimming in BCBS sitting around right now, if you don't mind the trip across state. Goose Island just released a couple more of their treatments of BCBS, their coffee variant and a new version aged in rye whiskey barrels with cherries. Should hit distribution soon for the states lucky enough to get some.