From an Eagle Scout.....
I spent some great years in Boy Scouts and camped over many summers at several sites.
My suggestions would be:
1) Be currently active somehow in scouting, even as an adult council advisor. If you have a specific skill, offer to be available to help the scouts earn merit badges or skill awards in your area of expertise to help them advance in rank.
2) If involved, volunteer for a weekend trip where they camp. The "summer camp" is used for many other weekends in the spring and fall for specific scout events like Order of the Arrow. Often the "old guys" as we called them hung around the fire and cooked for the scouts in the dining area when we were doing activities on these weekends. Bring the detector and hunt during free time. As mentioned just make sure it isn't historicial.
3) Each area has its own council, here is a link to find the council near your zip code:
http://www.scouting.org/localcouncillocator.aspx
4) There are usually several locations in a council were camping is done. Not all is at the "Summer Camp" location, though that is usually the largest. Often farmers offer land for the scouts to do specific weekend events at aside from the large camp. Ask where the local camporees are held.
5) There are often other areas scouts use hard when working on merit badges, bike trails, hiking trails, farms, church's, etc. Look at the scout handbook and also visit the local council offices.
6) Best advice is give to get with the scouts. There are many ways you can. As with many other places we seek permission it is a level of trust that must be built.