Just look in the backs of almost any sailing magazine and find about 3 to 5 manufacturers of compressor you can run from on deck, in the dink, or on its own float. Some may be able to operate two or more hoses. They have regulators and some allow dives up to 60 feet. You should take dive classes to use one of these especially if you intend to go deeper than ten feet. If you do dive deep I strongly suggest you invest in an emergency air bottle like the tiny ones James Bond used on more than one thrilling escape.
These systems are gas or electric and their advantage is that you are not tied to a refill station. For occasional bottom work or for retrieving a fouled anchor these are quite useful. Most offer water-tight containers for on-deck storage. Make sure you know how to maintain it and carry spare parts.