As mentioned, the original M3 has the biggest catalog of readily available spares, including an actuator for the central locking system, a clamp for the sunroof roof liner, and an M-Technic clasp badge for the rear seat backrests. These parts are shared with other models, while items like the upper part of the two-piece oil pan, some body panels, the rear spoiler, and upholstery cloth are exclusive to the M3.
The E31 BMW 8 Series is the only vehicle with serious mechanical components like a front axle reinforcement brace, a clutch disc, and a pressure plate, although the Z3 does have an engine mount. The E26 BMW M1 is worst off, with only latch strikers for either door available. Still, with only 453 examples built, this is the type of car BMW would surely produce custom reproduction parts for.
