Just had a look and the plastic is really cheap, less than £15 per Kilo!
There's a lot of places that do both 3D scanning and printing, would need to take a scan of the original lock covers to get detailed CAD image for printing dimensions.
If someone has a set of covers they could get scanned there could be some profit in selling low cost covers...
This is a list of places you can go to get them scanned (and printed) in the UK there's 63 of them! Anyone with a set of covers near enough to any of these places and wants to see if its doable?
https://www.3dhubs.com/3dprint#/?place=Birmingham,%20West%20Midlands,%20UK&latitude=52.48624299999999&longitude=-1.8904009999999971&distanceUnit=miles&materialGroups=prototyping-plastics&scanning
I think the price for printing could be brought down by emailing the 3D scans to a few different places and getting prices, from that website there are over 400 places in the UK that offer 3D printing and will post out the printed parts so plenty of competition in the market!
https://www.3dhubs.com/3dprint#/?place=Birmingham,%20West%20Midlands,%20UK&latitude=52.48624299999999&longitude=-1.8904009999999971&distanceUnit=miles&materialGroups=prototyping-plastics&shipping