Where can you buy a carbon fiber scuba diving tank?

Answer 1

There is at least one area in diving where the weight trade off might be a positive, and that is in rebreather diving. Using even aluminum tanks in some units will make a diver extremely negative when using a wetsuit, especially when necessary trim weights are added to the top of the unit to maintain horizontal trim. This results in much faster use of diluent just to fill the BC just to offset the negative bouyancy. A lightweight carbon fiber tank would be a great benefit. Even if the maximum pressure could not be obtained, as long as the gas volume was sufficient at 3000 psi, this would be an improvement over traditional metal tanks.

This has been talked about before - its a weight trade off. Your tank may be lighter but you'll need to weight down more somewhere else to make up for it.But they do use them in Turkey

Because Scuba tanks must be certified to be filled with compressed gas (usually compressed air) they have to be inspected by instruments with currently only inspect metal tanks. The tanks are manufactured in one of two alloys - pressed steel or aluminum. Even if you could find a manufacturer of a carbon fiber tank - you would not be able to get it filled at any SCUBA facility.