While submitting/looking at https://bugs.kde.org/show_bug.cgi?id=370384 I thought I would try to look at the code, but after getting the partitionmanager and kpmcore code I cannot seem to locate the "scanDevices()" function for the CoreBackend or CoreBackendPrivate classes.

Any idea what I'm missing?

CoreBackendPrivate is in src/backend/corebackend.cpp.
However, I believe what you're looking for is src/plugins/libparted/libpartedbackend.{h,cpp} in the KPMcore repo.