If you want a quick and cost effective way to jumpstart your prospecting, consider renting or buying a list. I’ve used a number of different services over the years and found that Concept Marketing is one of the best. They are available directly at www.marketingsource.com (this is not an affiliate link).
Keep in mind that traditionally to get any kind of response you must mail at least 7x to your list and provide a time sensitive offer (limited time isn’t enough, get specific with dates) and make it trackable with either a code or special word so you can measure results. Relying on someone remembering where they heard about you is, well, unreliable! This is by no means the only way to go but a good option to consider in conjunction with online marketing.