I have some experience with this.
I help mentor a high school robotics team. The school shop has a simple 3-D printer, we have printed parts and used them on the robot. You need to be careful not to overstress those.
At work we use a company called Shapeways to source prototype parts from our models. They are cheap and fast. The modern printers and materials can produce very useful parts.
A co-worker has Gemmy Animatronic Halloween figures. The arm-movement boxes tend to fail and Gemmy doesn't sell replacement parts. He pulled out a failed dual spur gear (appeared to be injection molded from nylon), I modelled it up and sent it to Shapeways. 5 days later he had 15 of them for less than $4. each and he hasn't had one fail yet.
https://www.shapeways.com/model/upload-and-buy/6699586
We have a Faro arm that we use to inspect and reverse engineer complex parts. We have also hired out laser 3-D surveying for complex projects, we haven't done enough of that to buy a unit. The "point cloud" output from that hardware can be very accurate but it takes some computing power to work with it.
Shapeways allows a resource to create and sell your own, "hard to find" parts at reasonable cost, if there is a market.