Those are
wondrous craftsmanship heavy maces, which still do occasionally drop in random gen. I had thought after the update 29 random gen overhaul that wondrous craftsmanship weapons had stopped dropping, but they still do (rarely) - I got this one last week.
The icon preview for the wondrous craftsmanship mace on the upper left (if you look closely) corresponds to your "maces of mystery".
I have been trying to collect different assorted wondrous craftsmanship weapons and armors to catalog whether any have unique appearances, but all wondrous craftsmanship items are btcoe, so I have been putting it off. I did try equipping a few wondrous craftsmanship robes and armors and - disappointingly - they just had standard random armor appearances. Jollysoul on Ghallanda had told me one time that either the wondrous dwarven waraxe or wondrous greataxe also has a unique appearance but I have been hesitant to equip the ones that I have to check (due to binding status).
I have to credit Andural on Ghallanda for informing me about the wondrous craftsmanship heavy maces a while back - he would be disappointed to know about this thread, since he is the only one on Ghallanda that I have seen that has glamered this mace look. He called them his easter egg maces.
Afterwards I started investigating other wondrous craftsmanship items to see what is out there.
yeah it is fascinating that they put out a unique appearance for the wondrous heavy mace.