On amazon. Installed easy enough. Picked up the marina wifi much stronger and identified a few more signals. Pretty flimsy though. I already sat on it once and almost broke it. However for $31 and free delivery it seems worth a try. The rogue wave units are $400 and I can't bring myself to spend that kind of dough for what I have heard is the same technology.
Would be nice if they had a longer cord but I imagine radio shack will have one.