The paperweight can be found in various buildings and ruins in the Capital Wasteland and the Mojave Wasteland and is sometimes sold by merchants. Since the Rock-It Launcher is not obtainable in Fallout: New Vegas, paperweights are purely ornamental in nature.
Paperweights are ubiquitous, but they appear more frequently in office buildings or at reception desks. They are also frequently found in the larger offices on the top floor of office buildings. One of the best places to get this is from Crazy Wolfgang. In Fallout: New Vegas, one can be found in Victor's shack in Goodsprings.