This might not be the only way to display your RPC libraries in Revit, but it works for me.
You need to place your RPC content into the folder....
C:\Program Files (x86)\Common Files\Autodesk Shared\Materials2011\assetlibrary_base.fbm\RPCs
For some reason, they have placed this into a 32bit folder (If you are working on a 64bit machine, it may have been confusing to find the path).
You will then see your RPC library, when you replace the RPC type.
For more RPC content, go to www.archvision.com