I am working on a project with a photographer where we are doing cyanotypes. i have a fibers/textile background and have a few insights i can offer you all.

Tannic Acid is present in many plant or tree-borne elements
Black Walnut
oak gall and sumac leaves
rhubarb root

this is why tea works so well is that it contains a number of similar ingredients
these elements are sold already processed through a number of natural dye suppliers
Earth Hues is a great one.

i will post additional suggestions once our experiments are complete.

for those that don't like the strong smell of vinegar can use citric acid
ammonia is also marketed to dyers in a form called Urea which doesn't have the horrible smell
these are easily obtained from Dharma Trading Company, i've even seen them sold at Dick Blick stores as well