I've never seen them for sale locally, but there is 12 Volt who used to have a monster 18"? or so pair(1 jumped so he has 1 left now) and a couple other members have been trying to find them. If you got the room and like big barbs I'd scoop 'em up. I don't think they're uber rare but not as popular as regular tin foils either.
Barbs are cool anyways IMO, giant barbs even cooler.