Demand a Title Insurance Policy. Title searches of the public records will also show liens or judgments filed against a buyer. The title company will likely ask for satisfaction of those encumbrances before it will insure the land contract on a title policy. Ask to see a copy of the preliminary title report (or commitment for title insurance) to determine if a search reveals anything about the buyer.
You can also look to certain companies and organizations that have a concentration of people that may fall in the above mentioned roles such as investment companies (i.e. Charles Schwab, Fidelity), financial advising companies (i.e. Morgan Stanley, Merrill Lynch). There may be a higher concentration of people who can both afford and want to build their own custom homes or to build income-producing properties. Try linking yourself to financial advisors who may already know of people who have these types of dreams. This isn't a comprehensive answer of all the possibilities but just some thoughts. Good luck!