DN Signs

I've owned my sign & neon company for over 10 years now. We have several clients with multiple locations. My business coach has been pushing me to actively prospect with small-to-medium sized chains. I have a pretty solid background in sales, but in 10+ years I haven't been able to crack this nut. The chains that have come to us have stayed with us, but I'd like to develop a more aggressive prospecting/marketing plan. Any ideas? I know there are services that provide higher-level contact information - i.e. Manta.com, etc. I've tried going through the main corporate numbers of a few chains but the gatekeepers there tend to screen pretty well. I've hired (2) sales consultants that have taken my money and delivered nada. I'm sure there are others here that have figured this out.