Hi there.
You asked about educational websites for postcard farming. You might try PostcardSmart.com. I publish the website, and I've written a couple of farming / marketing articles for agents. From the site's home page, look for the "real estate" link in the left-hand menu.
If you have more specific questions, feel free to plug them into my agent advice website (link below).
Also, Tanya brings up an excellent point. People like and respond to helpful information. With a little effort (okay, maybe a lot), you could develop a reputation as THE source of real estate knowledge in your area.
Just be sure you include a strong call-to-action with each piece you distribute (be it by email or postal mail). Information is great, but the real goal is to encourage a response, so you'll need to tell people how to respond.
Good luck!