There are actually several answers. If you want natural versions of their full size cobs, you'll need to order them directly from MM. If you want the best price with a discount for buying a dozen or more of the same model, Mars is the place to visit. Many other places sell them, but with the discount, Mars has the best deal for my money.
I agree with John, Missouri Meerschaum if you want natural versions, Mars Cigars otherwise. I get all of mine from Mars because I've found Mike at Mars to have superlative service. I've bought a lot of tobacco from him and also used to get all my snuff there before our congress critters screwed up on-line snuff ordering in the USA.