In order to spawn the wandering Debt Collector, you must of completed the side mission Sisterly Love. The mission is fairly easy and can be done early on after finishing a couple main quests in the Spendopticon.
After finishing the side quest, the Debt Collector can be located by chance through entering into The Spendopticon and will spawn where you finished the side quest. It’s quicker to travel from the Impound Deluxe, if he doesn’t spawn, travel back to the impound then save and quit to reload and try again. Happy hunting!