well, there is a simple recipe: blood, sweat and tears ...
I used a caliper to measure an original hood and then redesigned the parts using a CAD program (in my case I have access to a commercial CAD program).
If you want to use a free CAD program, you should select one which allows Boolean operations, i.e. you build the outer block and then subtract blocks to create holes and openings.
I don't think it is worth to consider 3D-scanning these simple parts as the results of 3D-scans usually require a lot of rework to produce usable parts.
Note that 3D-printing nowadays can also work with rubber-like plastics which have already been used to recreate working floppy belts (probably not a long term solution, but better than nothing).
Also complex rubber feet etc could be reproduced. Of course this is not real rubber and is likely to deteriorate over time, but again...