Hi, As Rob says, I'm sure the repro mud shields are a CCI exclusive product. If you want used genuine items, I'm sure CCI or Martin will be able to supply some. Although relatively expensive, the mud shields really do a great job of preventing mud accumulating in that cavity behind the front wheels.
The CCI ones are fine BUT ..... don't expect them to fit straight away, they will need trimming, holes extending & re-shaping even though when offered up to the originals they look good, I speak from experience
A very good idea to fit them though to stop crud attacking the metal work
It's not really a cosmetic surface under there & you're likely to be the only one to see them. Any old bit of tin sheet will do the job - use a couple of bits of cardboard as templates to make it easier. Some old rubber door/screen seals work fine for protective edging or a length of rubber tube/hosepipe so it doesn't chafe on the main bodywork. Extend the bottom so that it blocks road spray from the gap at the front of the sill.