I do believe that many (most?) potential short-sale Sellers really don't know or understand their options.
A lot of folks are too embarrassed to talk to anyone about their situation. Others are so deeply in denial, they won't even admit to themselves that they need help.
You could do some research to find homeowners who bought (or refinanced) during the "boom", and do a targeted mailing to them. My observation is that people who look like possible candidates for a short sale sometimes prefer dealing with a stranger, rather than a friend or relative who's a Realtor.
As Jeff suggests, if you have expertise in short sales, a blog might also be a good way to reach Sellers who might benefit from doing a short sale.
However, I have a concern about real estate agents giving short sale advice, since it's essential that most people considering such a move talk to an attorney as well. They need to explore all their options, and fully understand the legal implications of their actions, such as the possibility of their lender pursuing a deficiency judgment against them. Just my humble opinion.