Many sign companies can install them. Or you can use AOL Search to find Online providers of Electronic Signs.
HOWEVER, before you invest, make sure that it's okay with your town and county governments. A number of businesses in my area bought them and were threatened with fines for violating signing regulations. The local governments claim that electronic displays distract drivers. They, also, fine store owners for having banners or flags in front of their business, BUT the 30-foot inflatable Ronald McDonald and the guy in the mattress costume, dancing on the shoulder of the road is Okay!?!