Usually people in these circles looking for a breast milk substitute use goats milk. It has a good nutrient content and is more easily digestable than other animal milks. I know there are some companies making "natural" formula but i don't know how sound they are. Or look for a wet nurse. All are options good luck.

Sally Fallon's book, Nourishing Traditions, gives a few good options to breast milk. Her formulas make sure that the omega 3 content is in line with healthy breast milk and that other nutrient component ratios are in line with healthy breast milk. Sally is one of the most vocal opponents to soy formula usage for many reasons including the maganese content is about 80 times the level found in normal breast milk and because the phytoestrogen content is equivalent to giving a newborn 5 birth control pills a day.

Sally is not a vegan advocate as Schulze is, but she is a huge fan of whole, unprocessed foods, with a large percentage of the diet coming from raw foods. Her baby formula substitutes are the most well thought out of any I have ever encountered.

Also the posting with regards to goats milk is in line with my research as well. The nutrient profile of goats milk more closely resembles breast milk than cow milk. Also, if you can become comfortable with the idea, raw goats milk is FAR superior than than the cooked, pasteurized variety.