3D printing

Lots of factors. Here are a few.

• Do you have the original part? if you do, it can be scanned which "could" eliminate the need for cad, though some cad work will probably be required. it also might be the case the part is simple to draw up. Car parts weren't drawn using computers, rather basic drafting techniques so it's likely not that hard to draw up.
• Does it need to withstand heat? The material makes a difference since most 3d printing is done with melted plastic, it doesn't take much time in a hot car to weaken/warp them. Resin might be the way to go but I don't have practical experience with that.
• How strong/flexible/ridged does it need to be? Again, material/method choices matter.

if you have the part and it's not huge, you can "fix it" using body filler or whatever and make your own silicone mold. Lots of videos of how to do that online.