1) During the second 'Yay' Money to San Fierro mini-mission, the Grove Street couriers drive a tan, notch-back Patriot.
2) Respond positively to the phone call from Cesar initiating this mission, then drive quickly to your stored tow-truck, ignoring the Patriot.
3) Once in the tow-truck, track down the Patriot and follow it to the end of the mission; triggered by the Patriot being bumped, dropping all its cash.
4) It helps to pull ahead of the Patriot at some point and snipe his gunman only, the driver is otherwise invincible, and the Patriot's door is locked.
5) When the mission ends, the Patriot will drive-on but now only as a fairly normal vehicle, both driver and vehicle are still secure, but free to take by other means.
6) So, follow the Patriot closely until it eventually hits another car. Its driver will get out to fight the driver it hits, at this point sneak in, hook the Patriot with your tow-truck and drive off.
7) Once the Patriot is safe in your garage it unlocks. Take it for a spin and show off your new Bullet-proof, Bomb-proof vehicle.
8) Hardly a stolen Hunter
, or first day Seasparrow
but defense is the best offense
Additional: This Patriot, unlike the LC bullet-proof Patriot appears to also be no fault collision-proof. If I hit something it does damage to the vehicle, but if something hits the vehicle, it does no damage at all. I did donuts on Ganton's main avenue for ten-minutes and saw more than one police car explode, just from ramming into me.