I've generally only volunteered for something when friends of mine were already involved. College students, if you have them, are always great targets.

One short-cut is to approach existing groups. Churches, civic organizations, neighborhood associations, clubs (rotary, masons, ham radio, bee-keepers, etc.), even scout troups. If you can get one gung-ho committed person, they can likely bring you 10 others.

One of the worst aspects of dealing with volunteers is that they don't all pop out of the same mold. You need to be ready to find ways to use whatever you get. (Or have a way to make it clear why you can't use them.)

A great book to read is Robert B. Cialdini's Influence: The Psychology of Persuasion.