It's always fun talking about legacy software. You're right, the filenames are available, but not the content.
Not sure if I can help, but these guys seem to have it available, but really expensive.
If you can prove to them that you purchased it, maybe they can offer those files.
Emsps doesn't seem to have version 3, but maybe some of the source from earlier versions is similar
You might be able to try TheGrideonSoftware Zip Password app for decrypting legacy zip files.
I purchased comix way back, but am almost certain I didn't purchase the latter versions of the Six rdd.
The only other thing that comes to mind, is if you have any executables built from that library, or if you have the libs or obj files to build an executable, then you can use Valkyrie to recover some of the functions you're missing.
Also, perhaps some of the Harbour source might provide some clues.