Hive account@lextenebris is spot on. Unless someone else has CAD designed an auto part and posted it on a site like GrabCAD, then you'll have to make it yourself and print it. Then with respect to printing metal, it is best to shoot for the higher end printers like the MakerBot Replicator 2 which can print in metallic.

If you're looking to do one-off custom prints of rare parts than this is the way to go, like for a 1913 Mercer or 1929 Duesenberg it would be perfect!

Keep the faith!