If you know pretty much where they are you can do it this time of year with a good wetsuit. I did it a few years back getting a boat off the bottom. Was probbaly down for 10 minutes in 45 degree water at False River just using a wetsuit and a neoprene hood. Be prepared to have a way to warm up after, but if its just a simple down and sweep a small area you can do it with some shrinkage of course :)
There is a guy from Laffite named John Estes who dives ,not to be confused with John Estes the shrimper from da'Parish, he helped me get a shrimp boat up that I sank one winter and he seems like he really does it for the adventure and love of diving as he only charged me $200 for a long days work , I dove on the boat myself as I am a certified diver and dude it was rough , I was so tangled up in wing net and rigging with a couple of thousand pounds of shrimp in zero visibillity water and I kinda freaked and had enough so I called him in ,if you want I could dig up his number
Sorry I didn't report back I recoverd the guns I found the benelli 5 month latter and the beretta 7 month . They would still shoot and no rust they were in fresh water . Anyway here is what I learned . The were not in floating gun Casey's thank god. Because they were only about 7ft from were we turned over :........................from now on. My guns will be in floating gun case with a steel cable hook to the boat . You can find the boat
try your local fire dept. now the fire dept itself wont help you, but Im sure one around you has a dive team and divers love to dive. so maybe for fun or even training they may would help you out. its worth a shot