• Historical Societies
  As a general rule, Historical societies may not have the funds to do cemetery restoration and as a result may be unwilling to get involved in the cleanup of one specific cemetery for fear that it may mean having to restore all the other ones in their county. However, this is not the case in all areas and you should contact a local Historical society to find out their specific policies.
• Genealogical Societies
  If there is a local or County Genealogical society in the area you should by all means contact them. In many cases, they will be ready and willing to assist in cemetery clean up and restoration projects.
• Historical Preservation Groups 
• Boy Scouts
• Girl Scouts
• DAR - Daughters of the American Revolution
  If you can prove that a veteran American Revolution is buried in the cemetery, you might be able to enlist them for some assistance.  However, more often than not it's been proven that they are unwilling to get involved 
• SCV - Sons of Confederate Veterans
• Veterans Organizations
• American Legion 
  In some cases, they may also offer funding assistance for repairs to cemeteries where veterans are buried.
• Local Kiwanis Club
• Local church youth groups
• Community Service workers  
  The use of people working off "Community Service" sentences (non-violent offenders who are sentenced to work off X-number of hours of community service). These can be a ready source of free labor, especially those folks who want to work off their community service sentences on Saturdays because they don't want to lose time from their Monday-Friday jobs. Check with your local law enforcement to see if this option is legally available in your area.
• Inmate Labor Crews
  More and more, groups are working in conjunction with the County Sheriffs. They are pretty willing to provide supervised inmate labor. These are not "chain gangs". Doing this kind of work is purely voluntary. The inmates get to get outside for a few hours, they get some fresh air and sunshine, they get some exercise, they get to do something productive, and the community benefits from their labors. These crews from the Sheriff's Office can also be very important to long-term maintenance of these cemeteries after the initial clean-up is done. Check with your local law enforcement to see if this option is legally available in your area.
• Media coverage
  Place an ad in a community newspaper, see if your local radio or TV stations will place a public service ad for you. People want to be involved, they have just never been asked. And you never know who may show up. 

Free labor means you can dedicate what financial resources you are able to muster to materials, supplies and professional services. No matter where you get your volunteers from, one thing that you should do is to provide lunch for these crews --- such as  deli sandwiches and soft drinks.  

One vital thing to keep in mind is that in most, if not all cases the free labor that you will find from these and other sources will be untrained in the field of cemetery restoration. For this reason alone, you should plan attending at least one stone repair workshop where you can see first-hand how repairs are done in usual circumstances prior to starting your project.

And don't forget approaching local businesses up for donations on materials and supplies -- mortar mix, sand, gravel, shovels, etc. Be sure to give the donors lots of free publicity.