If you are from New Jersey, you can begin your search online by reading the local Sullivan county newspapers (Real Estate Section) . Look for Farms for sale, and the broker who is selling them , and give the broker a call. Here are the local newspapers: River Reporter:Narrowsburg. Times Herald :Sullivan county (ulster) and delaware. Sullivan County Democrat. This will get you started.
Your best bet is to contact a local Realtor that has access to Multiple listing services and has knowledge of the market area. He or she can send you up to the minute listing information on all available properties that meet or match your criteria. They will also research properties that are not currently listed on your behalf to find a potential match.