You should be able to find blue berry extract at any Homebrew supply and you can definatly find it on one of the big online stores (more beer, northern brewer, austin homebrew, ect...). IMO, I would use fresh fruit, in your secondary. I am not a huge fan of the extracts. I haven't had this beer, does it have a blue color to it? If it does they most likely used real blue berries. if not then Probably go with the extract. Post a recipe if you turn out a good one.
"Yes, I am a pirate two hundred years too late. The cannons don't thunder there's nothin' to plunder,
I'm an [under] forty victim of fate, Arriving too late, arriving too late."