'Getting something like that is so simple my friend.......contact your local arts commision........have them put you in touch with mural artists and other artists in your area..........look at their work, pick one and make your building a landmark.
You could even save money and showcase your standing as a community leader by getting in touch with your local high schol or college art instructors and/or departments and letting student artists use your building as a large canvas..........and then showcase and show off their work in your advertising.
[ EDIT: Just to give you some inspiration........we have a well-known local artist known professionally as "Blue Sky" He has done quite a lot of work here in Columbia, SC.....Here's some of his work....on the sides of buildings I might add ]