There are numerous Web sites out there in cyberspace that list forest land for sale. Other excellent sources of information include professional consulting forestry companies as some consulting forestry firms specialize in forest land real estate transactions. This will likely be your best bet!
Each state has a list of professional consulting foresters--all you have to do is a little Web surfing :-) Not to mention, many consulting foresters and consulting forestry firms operate their own Web sites.
Best of luck!