CampingFan:
There are many internet sources helpful in finding volunteer camp host positions, in addition to those mentioned above. An excellent source is the State Park web sites. Sometimes they are a bit difficult to find, but they are generally out there. City and county parks with campgrounds use hosts too.
Then there are other similar volunteer positions, besides hosts. For example; Boyce Thompson Arboretum, just outside Mesa AZ utilizes volunteers but has no public campground. We will be volunteering this winter at Patagonia Sonata-Creek Nature Conservancy at Patagonia, AZ. They have no campground either, although they do provide a full hook-up for a volunteer.
Our success in finding volunteer positions has been through e-mails to the park. In the e-mail I explain something about our background, health related restrictions, interests, and our availability.
Good hunting!