Dear Brian:
I do not know of any reliable sources in the Dallas-Fort Worth area that handle everything you are looking for offhand, but there should certainly be one or more marine aquarium societies in the area that would be more than happy to point you in the right direction. I would suggest contacting the local marine aquarium society and asking them to recommend good sources in your area for the items you are seeking.
Of course Ocean Rider (seahorse.com) is the only source of high-health seahorses that are guaranteed to be free of specific pathogens and parasites, and they can have their livestock delivered directly to your doorstep overnight via FedEx priority shipping, but Ocean Rider does not deal in items such as live rock and/or live sand because the shipping costs from Hawaii for such heavy items would be prohibitive.
Best of luck finding a good source in your area for everything you need, sir!
Respectfully,
Pete Giwojna