Since milk snakes are typically not considered a threatened species, it’s going to be tough to find any conservation efforts that are specific to milk snakes.
The best way to assist with conservation of any wildlife in this country is habitat preservation. You can’t save a species, but you can help preserve entire ecosystems, and all the flora and fauna within. Groups
like the nature conservancy (www.tnc.org) are in the business of preserving habitat.
Education is a powerful tool for one of the other threats to snakes in general and that is intentional kills by man. The more people understand that these animals aren’t out to get them (or out to milk their cows!) the less likely they are to seek and destroy. The general public can be a strong ally or foe.
There are a few good herp conservation organizations on a national level that you may want to look into:
PARC (partners in amphibian and reptile conservation, www.parcplace.org) the Center for North America Herpetology, www.cnah.org, and the society for the study of amphibians and reptiles (SSAR, http://www.ssarherps.org/) are good groups to check out and support.
Good Luck, and I admire your desire to get involved in conservation.
Dean Alessandrini