onlinerack,
I think it's called velvet tamarind (
http://en.wikipedia.org/wiki/Velvet_tamarind)
. I have no idea where you can get the fruit, but here's someone selling the trees on eBay, they might either know, or even have some available from time to time:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110527041307Cheers,
LHerrou