Google is your friend:
https://google-sketchup.de.uptodown.com/windows/download/4660
The older versions are sometimes hard to find so it may require some more work to dig them out again. If you need a copy I suggest downloading it and saving the installer to different mediums to be safe. I personally use SU 6 and 8 and have several backups which should save me much time in case of a crash.
Alternatively you could use one of the latest versions from here:
https://www.sketchup.com/de/download/all
The Pro version requires a license ($$$), the Make version is free and should offer enough functionality for the happy paper modeler.
The files are not backwards compatible, so files saved with SU7 cannot be loaded in SU6. This can be solved by dropping down the saving dialogue and choosing "save as SU (whatever-you-need)".
P.S.: Old thread > locked. If you have any more questions, please feel free to start a new one.