The internet has made it possible for creative professionals to generate client lists for nearly every market and forum that their individual work is applicable to. There are some great resources such as Agency Access and, now under the same umbrella, AdBase that offer marketing services to thousands of contacts for a subscription fee. But if freelancing in a down economy has left you in a less than lucrative situation and you're looking to cut some business expenses (or your free trial has expired for either of the previously mentioned sites), well then it's time to roll up your sleeves and get down n' dirty with the periodicals at the local book store.
Most magazines will openly divulge most of the information you need to generate a successful promotional campaign in its masthead; art directors, creative directors, editors, publishers and other people you may want to contact and start a business relationship with. Any information not supplied by the magazine can usually be found through some further digging in the "about us" or "contact" pages of their company website (Hint: it is not common practice for email addresses and phone extensions to be printed in the magazine). This method of finding clients is also a great way to customize your campaigns, marketing to those that publish your style of illustrations or where you feel your work will be a nice fit. Simply flipping through a magazine and finding some spot illustrations will usually give a good indication of the tone the publication is going for. So, grab a stack of magazines, a sketchbook and get ready to write down as much information as you can handle...then write down some more. If you get bored, just draw some random people in the café for a while then get back to finding clients!