Where can I buy sacks of live crawfish in Dallas
Here is a link to a similar question last year. The OP was looking for more restaurant recs but there are a few retailers also.
All Texas Farms Open to the Public (if you care to see where your crawfish come from)
http://www.bridgecityseafood.com/ (Has a restaurant, market and charter services – even a catchy Cajun theme song on the website
Doguet's Crawfish Farm
16939 Highway 90
Beaumont, TX 77713
Tails R Us Crawfish Farm
3202 Farm to Market Road 2936,
I do know that when in season Central Market, TJ'S, Seabreeze, Fiesta, Crawfish Hut inside the Saigon Mall, and many local retailers will have them available.
Local Places most of which carry Louisiana crawfish
If you are looking to keep your selection within the United States (i.e. Louisiana and not comprehensive)
http://www.crawdads.net/ http://www.lacrawfish.com/ (Same company
A more comprehensive list from Louisiana Crawfish Promotion and Research Board
I've not puchased crawfish at Fiesta or any of the Asian markets so I can't speak to those but I will say that TJ's is a true fishmonger and they provide the highest quality in the seafood they sell. They sent out an email last week saying they would have crawfish soon but they would be expensive and would price out much better as the season got fully underway. As DD said, they are very accommodating and service oiented as well. Located in the southwest quadrant of Preston & Forest. Rex's Seafood at Lovers Lane & Inwood is another true fishmonger with good quality and good service and they probably have them as well.