When you install a mod there's no preserved record of the dependencies. You'd need to scrape those from the references generated by opening the mod. It shouldn't be hard to make a Mapper's Dream tool for mods since UCC generates a dependency list as it tries to open the file.
TBH there's probably not very many mods you could find that someone in the community doesn't still have the zip for. The very earliest ones didn't even have zips though. It was common practice to allow players to idle on your server overnight so they could get copies of the maps and mods since there were not many download sites. A lot of the early developers just put their stuff on servers and that was how it was shared. You got to remember this was the days of public bulletin boards because actual forums weren't a thing yet. For a bunch of the earliest Unreal content there exists only cached versions. Thank goodness people like Hyper saved everything over the years.
"You damn kids, back in my time we made the items, maps and games ourselves with an unwieldy engine using counter-intuitive crash-prone tools and we liked it so much we built communities around this which nowadays look like cults because they're quasi-parallel societies based on the same old games." -Hellkeeper