Ask around the Town Hall if there is one. If not, try asking around the Pittsburgh Town Hall. The latter is more of a stretch so I would check other options before making the trek if possible.

You can also try the Sanborn maps: https://www.loc.gov/collections/sanborn-maps/about-this-collection/

The LoC collection is very fragmentary (and Michigan-centric for some reason) and seems to not have your town. But I looked harder and found that there was a collection of Pennsylvania maps hosted by Penn State: https://collection1.libraries.psu.edu/cdm/search/collection/maps1/searchterm/Oakmont%21Sanborn%20Fire%20Insurance%20Maps/field/geogra%21collec/mode/all%21exact/conn/and%21or/order/nosort