If you actually DO have HQ render files for your original media, then you would find them in the Events folder, not the Projects folder. You will have to know exactly which events you "took" the media from.
If you do find the rendered copies of the clips that are missing, Copy them out of their location in the Events folder by holding down the Option key and click-drag the files to another location (quick duplication with move operation). The Event (name) > Category (or "sub-event") Name > Transcoded Media > High Quality Media render clips should have the same name as the original video clips they were made from, which, I would assume, would allow you to "reconnect" the media quite possibly as easily as placing the new copies in their original locations (and restarting FCPX if it is running.) Otherwise, manually reconnect the media as necessary.
Actually, Project "render" files are in the Project, and not in a video format.
Compound and individual clips "render" in their own timelines are in the Events folder, and in the same non-video format.
"Transcoded Media" are not the "render" files the OP is referring to. The "render" files can not be made into standard QT files.
If you have no Original or Transcoded files, you have nothing. My question is, "how" did you lose the original files to start with? That would give us a clue to proper proceedures in recovery, if possible.