If you do not want to spend money for this vehicle, you can acquire it during the side mission, available for Micheal, and its spawn location is most likely to be active. To start this side missions, pull up in-game mobile as Micheal.
Type Epsilonprogram.com on internet page, then press the “Evaluate your identity” option and complete it. Micheal will receive a new contact in Raton Canyon. Following the mission line, leads you to mission where you should drive 5 cars to Epsilon garage. At this point Pegassi Vacca should be at location in Vinewood Hills, in a parking lot, which is a backyard of the biggest, white house in that area.