Simply follow the graph below and you will be able to select / find / identify all those imported dwg files. Its easy and it only takes 7 nodes.
If you want to select these imported dwg's in Revit you could simply select them by typing in the element ID from the DynamoBIM filtered list into the "Select by ID" dialog box in the Revit Manage Tab. I hope this helps and happy imported DWG hunting!
A special thank you goes out to Dimitar Venkov for helping me simplify this Dynamo graph!