I use the Jarrow's formulation
here, but it's difficult to say that it's doing anything.
Our gut bugs make K2 as a byproduct of fermentation, so basically more bacterial diversity = more K2 production. Short of supplementation, I suppose expanding our microbial profile would be the best way to get more k2 in our bodies. Antibiotics short circuit this production chain and increase the risk of every problem, osteoporosis included (kind of wish I knew this before taking them).
As for as sources - ideally, it's probably best to get it from raw dairy (kefir, butter oil, raw milk, cheeses, etc) or fermented soy like the japanese do.
Chris Kresser did a nice
piece on it that might be useful:
On the other hand, fermented foods, however, such as sauerkraut, cheese and natto (a soy dish popular in Japan), contain substantial amounts of vitamin K2. Natto contains the highest concentration of K2 of any food measured; nearly all of it is present as MK-7, which research has shown to be a highly effective form. A recent study demonstrated that MK-7 increased the percentage of osteocalcin in humans three times more powerfully than did vitamin K1. (Schurgers & Vermeer, 2000, pp. 298-307)