Where can I buy fresh water prawns? Seafood Watch persuaded me that I ought to experiment with fresh water prawns in my cooking.

Problem: I'm in central Texas, and I can't find any.  The local fish markets and grocers offer no leads, and I've failed to find any good options for having them shipped on line.
Remember that a lot of this seafood naming is odd sometimes. Prawn is often used to refer to what we used to call shrimp.

In the UK I get these in brine from my local supermarket, marked "krabben im lake" or something similar ...