Depends on the plane manufacturer as there were quite a few different types of Zinc Chromate used.Find one in a modellers paint,paint a sample then get a paint shop to match it as Streakeagle noted.
Or try Ebay if your crazy enough.
https://www.ebay.co.uk/itm/De-Havilland-Mosquito-Box-Throttle-Quadrant/284083139719?hash=item4224acb487:g:wg4AAOSwys9fspvy
I did some knobs for an ex friend who has an original Mozzie Quadrant.Try the Historic Airplane forums for photos,manuals or plans.Only a few companies in the world have rebuilt Mosquitos.
https://www.warbirdrestoration.co.nz/past.html#ka114
I can highly recommend Stangs P51 CAD drawings.All the P51 parts Ive made have come from his work..
https://www.shapeways.com/product/L2L948A6E/k14-reticule-control-p51?optionId=63433387&li=shops
Ive bounced between metric and Imperial all my life..The magic number is 25.5 or going the other way 0.0393700787401575 :)
Problem is today the majoritory of CNC/Laser and Waterjet cutters prefer Metric.
I just got the final pieces together for some P51 throttles.The company who does my waterjet company got snowed under so put me behind.And yes they have the K14 twist grip.
I like the look of the new Replica controls!
They have a sticky setup at Checksix
http://www.checksix-forums.com/viewtopic.php?f=286&t=189628&sid=688b3f460c6c69a5b05692bf501a2368
Problem with sharing 3D files is that it takes business away from the designers who have the parts up on Shapeways.We get upset when our hard work gets passed around for free and we dont get any acknowledgement.
Sometimes it takes weeks or months of unpaid research in doing rare and complex part designs.