How to export the XMP from the Lr (not LrC)

Hi Lightroom community, 

I need to (ideally) export the sidecars only from the online album in the Lr.

I have lost parts of my edits and the originals from the Lr Classic. I still have the unedited raws saved externally but the edited files only exist on the Lr online albums. When I try to export + setting (to get the sidecars) Lr only exports the dng files, and as a small preview only, no side cars. 
My theory was. I will export the sidecars from the Lr online albums, add them to the old raw back ups, and import them back to the LrC albums with sidecars, the edits will then re-create... this does not seem to work though.... Any thoughts on how to achieve that? 

Or is there any way to add the original raw to the online album so that the edited versions kind of "sync in" with them? I didnt find the option of "locate file" like you can do on the Lr classic when you move your files around and only the previews remain in your collection. 

Any suggestion appreaciated