Generally speaking, if you have the skillset/equipment to make 3D printed parts or 3D models, you're better off making your own designs and selling them openly on shapeways or something, vs trying to illegally sell them on the down low to a much smaller, much less trustworthy customer base.
Also, 3D printers that are on par with traditional manufacturing are expensive and rare, there's a reason third party bits makers that have access to high grade printers will often use them just to print out the master models and then make a traditional mold for the actual production (I know that's how kromlech does it).
Popgoesthemonkey is probably your best bet for shoulder pads or vehicle insignia.
