One product called Bio-Red contains 12% Azotobacter. From Wiki at https://en.wikipedia.org/wiki/Azotobacter:
Azotobacter is a genus of usually motile, oval or spherical bacteria that form thick-walled cysts and may produce large quantities of capsular slime. They are aerobic, free-living soil microbes which play an important role in the nitrogen cycle in nature, binding atmospheric nitrogen, which is inaccessible to plants, and releasing it in the form of ammonium ions into the soil. Apart from being a model organism, it is used by humans for the production of biofertilizers, food additives, and some biopolymers. The first representative of the genus, Azotobacter chroococcum, was discovered and described in 1901 by the Dutch microbiologist and botanist Martinus Beijerinck. Azotobacter species are Gram-negative bacteria found in neutral and alkaline soils,[1][2] in water, and in association with some plants.[3][4]
14 % Clostridium
https://en.wikipedia.org/wiki/Clostridium
Clostridium is a genus of Gram-positive bacteria belonging to the Firmicutes. They are obligate anaerobes capable of producing endospores.[1][2] Individual cells are rod-shaped, which gives them their name, from the Greek kloster (κλωστήρ) or spindle.
I don't know how it relates to nitrogen fixing.
A product on Amazon containing Azotobacter:
Hydro Organics HOR00750 4-Ounce Bio Zeus Earth Juice Plant Supplement
http://www.amazon.com/Hydro-Organics-HOR00750-4-Ounce-Supplement/dp/B007F86RN4/ref=sr_1_14?ie=UTF8&qid=1434846249&sr=8-14&keywords=Azotobacter