I’m working on better ways to do this, but currently you can find the link sources if you paste the record link as plain text (i.e. Paste and Match Style) into another record or note. In that case, you can follow the link by selecting it, Control-clicking, and choosing Open URL. To find the records that have that link, you can do an Anywhere search for the record’s GUID. For example, if the link is x-eaglefiler://open?library=~/Documents/EagleFilerTest/EagleFilerTest.eflibrary&recordGUID=t8GEz67fSEyrXW883UVPqg you could search for t8GEz67fSEyrXW883UVPqg.
In EagleFiler 1.9.2 (currently in public beta), this now works for regular clickable links. You no longer have to use Paste and Match Style (except if the link is in a note).