Considered marketing? Find a good source that handles printing up postcards and mailsorting them for you, so basically you just pay them money and they print, address, and send them out. Buy a address list, and send out a mailing advertising a mass mailing service. Say on the postcard you send out "If you're reading this, it works. Get your company's name out there, just pay our company $XXX and we'll do a drop like this for you too".