There’s plenty of watches you can get from the abandoned camps, and other such breakable items. However, there are many guaranteed spawns in the Leisure Bunker, which connects to the 3D printer cave. You can always go for a run through that bunker and grab the watches on the sofas and tables.
When you’ve done a run, feel free to save and reload the save. That way, the spawns will refresh and you can go back in and do another run for it.