For some landowners, the idea of working with an agent is appealing. Real estate agents, especially those who specialize in land sales, know the market well and can help you get a reasonable price for your land. But the problem with working with an agent is you have to wait for the buyers to come to you. When they do come, they are often the ones dictating the terms of the sale, meaning you might end up getting less for your property than you had hoped.
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!