Do NOT buy from Saltwaterfish.com they are not worth spending the money on that poor octopus! They abuse their animals! My last 2 octopus were from that place and they are not worth the $$$ you spend on them! I had to save one of them and the first one -died-! Please take our advice and shop from one of our own tonmo members or elsewhere! They have terrible service if you need help!
"Carribean" octos seem to be what's easy to get right now. One of my LFS has had a few lurking in some of their tanks. From what I can see, they have all the looks of a vulgaris but don't seem to get as large - a female they had got to be about the size of a softball before brooding eggs. But, that was just my one experience seeing a Carribean one up until brooding.
There is the Atlatic pygmy octopus (don't know the scientific name), O. Mercatoris (A dwarf species), and O. Briareus. I believe these species mainly live in shallow reefs or caves, but that's all I could tell you about them.