You 'might' be able to find replacement boots but it's a long shot. If the joints themselves are still serviceable just keep them greased on a regular basis. All the dirt and junk going into them will seriously shorten their lifespan so buy a set of joints and put them aside for the day when they start clunking and your steering starts to feel tired and sloppy. Chances are the ball joints are already worn out - check the control arm bushes as well visually and with a pinch bar. Some of these poor trucks go above and beyond the call of duty