Most national companies have established vendors throughout the country. If the national company happens to receive work in a certain area, those vendors are going to get first shot. If they don't currently have a vendor, the project managers will seek out a vendor that meets their requirements (insurance, etc.). Most will seek out that vendor through a simple Google search, through sites like SignSearch or by reference via another nearby sign company that has likely used vendors in that area.
So if you're wanting work sent your way from national sign companies, you need to fall within one of those (or other) parameters. The thing is, though, national companies won't receive a ton of requests for the smaller type jobs you're referring to that are out of their area - it simply isn't cost effective. The customers needing that kind of work (smaller digital prints, etc.) will typically contact a local sign company. The case where this may change is if a national handles a nationwide chain (ie: AT&T). But even then, there is usually more than one sign company approved to handle work for those types of customers. Usually another national will already be assigned to that region.
