hey how far do you lie from the coast ? try fishing for them in the marsh with a fine net then just ween them off of salt water to fresh thats what i do here in ny
i get them from the swamp i duck hunt. like said before use a fine mesh net and drag threw the grass and push it around bush could usually get thirty to fourty a trip. not to mention a few crawdads and trap door snails
Idk if u can change the shrimp from salt-fresh but u could buy a cast net then go to that cosway thing between Corpus and Portland and you will catch tons of Shrimp there.