I think that what he's saying is that while yes people on here do exchange advice on material, equipment and processes, what it sounds like you are asking for is a client list. This a pretty sensitive to everyone here as this is how they make their living and with the relative low cost entry into this industry now more and more people are fighting over the same dollar.
I understand what your asking but there are people on here with these accounts that might be in your area and you basically asking for help in stealing a client, which is kinda a dick move. Also the way you asked your question didn't help.
As far as actual
signs, I can't help you as I'm not involved in lighted
signs, but there are some places that you can become certified an register on a national list such as 3M, Lowen, Avery, and Oracal that national companies contract out. I'm sure there are similar sites for lighted
signs as well.
Also be aware the these national contracts usually are bottom of the barrel and dealing with them is frustrating to say the least. You might just be better to go to the building manager.