I recently met with the Small Business Development Center which I was referred to by my local Chamber of Commerce. During my meeting he suggested pulling a list of all the companies in the area with 5 or fewer employees (as these would be most likely to need a VA). Well, I received a list with over 3,000 names. I've of course narrowed it down by company type and just sent out my first 100 mailers. (keeping my finger crossed for some postive results).
Anyway, this list was FREE and in excel so it was super easy to print mailing labels. Your local Chamber is a great place for free resources.