I found this info during a quick search. The good part here is that we have the name of a co-author. Perhaps he can be tracked down.
https://gamesdb.launchbox-app.com/games/details/97923-dungeon-adventuring-constr...
Viewing post in Actual PC version of C64 Dungeon?
Ah, that co-author listed is Jon Mattson. I don't think he was a co-creator, he made two of the adventures LOADSTAR published for Dungeon. He was a prolific LOADSTAR contributor and made several other programs for it, including one game system of his own. But Dungeon predates his time with LOADSTAR, I think.