U joints, slip yoke, and support bearing

Why do they make it so difficult to find these products for these vehicles? Numbers on the old parts don't match up to anything i see online . I've got some u joints from local part store but IDK if they are the right ones. Also a support bearing. But the slip yoke i still gotta order. Because i doubt anyone has ones in stock. Any guidance available out there? I'd prefer Spicer products. T I A