I've wanted to try these things for a long time; was under the impression they are not imported legally due to some pest problem or something. Anyway I was in the Thai Market across from the Safeway in Silver Spring last eve and fell into conversation with the young lady at the cash register and, lo and behold, turns out they have them, the real thing. They are, however, frozen, not in a platic bag but the whole fruit in the shell just frozen and sold 10 in a net bag. She said, and I have read since, that this is a OK way to preserve them--pretty much the same as fresh once thawed.
Maybe others have found these things around town, but it was a first for me.
You thaw them overnight. The fruit is pretty good, hard to describe sort of a rich tropical flavor slightly sweet and a bit of tangy sourness all rolled into one. Not very much of it tho. The whole fruit part, once out of the thick shell, is about the size of a ping-pong ball.
They were $4.90 for a bag of 10.