Depending on the "sunshine" laws of your state regarding public documents, the plans should be on file at the city or county department that issues building permits. Be aware though, that in most cases they are just that, plans, which show the footprint of the building and lack side elevations. When I got a building permit for my house, I submitted only a plan and the front elevation. It was the following year before the county required all elevations.
It is possible that if you get the name of the architectural firm that designed the building from the county records, that firm might still have the elevations and possibly be willing to share them. If it's a 100 year old structure, I wouldn't count on it, though.