While this may not be the easiest solution available, it will allow you to obtain a list of file names through the program and then use that list to select the correct RAW files accordingly.
Best of luck.
By "sort through the photos", do you just mean selecting which ones to import, or have you also done things to the photos - like keywords and such, maybe some image edits? Also, have the images been renamed after import, or moved into different folders after import?
First, there is a setting in LR Preferences "treat JPG files next to raw files as separate photos". I think you are going to need this option checked, to sort out the present situation.
Next, assuming that the original batch of camera images (Raw + JPG), from which you have imported only chosen images, is still separate and identifiable somehow - for example, a given folder on disk or on the camera card. You can import all those Raws and JPGs together, in the same way as previously (into the same place as the prior import), and then sort things out from there.
In doing so, LR will detect that certain image files are already imported, and avoid trying to import them a second time.
But before that, you'll want to have somehow "marked" the JPG images that you have got imported currently, to distinguish them. Assigning some special unique keyword, a distinctive colour label, something like that.
So you've got a whole lot of JPGs and a whole lot of Raws (within, say, a certain folder) and just some of the JPGs are "marked".
Now you could obtain the plugin Syncomatic https://www.photographers-toolbox.com/products/jbeardsworth/syncomatic/
(disclaimer: I have not yet used this one myself) and then use it to transfer settings from all the JPGs in that folder, onto the corresponding Raw files. That will include this new distinguishing "mark" whatever it is, in cases where it has been applied. And it can preserve whatever other work you have invested in those same photos. This presumes the file names match up, aside from the differing file extension - so if you originally renamed the JPGs when you imported those, you will need to rename the Raws according to the exact same scheme.
Now you have got a lot of Raw and JPG pairs, and for some of those pairs both versions are "marked", and for the rest of the pairs, neither version is. This gives you selectivity to Remove all the unmarked thumbnails, Raw or JPG, from the Catalog. And you are left with both a JPG and a Raw for the photos that you do want, with settings matching in each case. Now you can filter out and Remove the JPGs leaving the Raws in place..
richardplondon -- Thank you for the feedback!
By "sorting through the photos" I mean selecting which ones to import along with some low-level keywording.
I'll give this a shot and report back how it goes.
I've had another thought - far simpler.
In your Import window, grid view, all the JPGs that are already imported will show dark. If sorted by filename, a related JPG and Raw fall adjacent. So it should be relatively rapid to un-check all images, and then to click and accept (P) for import, just those thumbnails which sit next to a darkened thumbnail. Those will be the Raw versions, from each desired pair.
Then you could (optionally) use Syncomatic to transfer your keywords from each JPG onto its related Raw.
Then (optionally) remove the JPG from Catalog.
THAT, sir, sounds like a winner! Thank you!