Searching through trash cans (Law Enforcement/Private Investigator career), using the Miner (created with Inventing), can also give Woohooium. However the two most efficient ways to get it are hunting with dogs and sculpting with a sculptor who doesn't have the "Savvy Sculptor" trait (you get it a lot when you break stone blocks while sculpting).
Hunting is definitely the most efficient of the two, though.