My'53 Plunger came with mudguards having a central rib, and this appears the original style for that year. The hinged rear guard was missing the hinged bit, the rest was made of rusty lace and (foolishly) consigned to the scrappy.
This was in 1976, and universal guards were readily available, and I adapted a rear guard to fit. It had no rib, no hinge, was a bit short, but I extended the front and made the indent for the chain. The rear stays were also missing, so here again a bit of steel tube and flat strip came to the rescue. Finished and sprayed up it has passed scrutiny for the last 40+ years.
If you just want a useable bike, this is the way to go. Otherwise a case of finding a reasonable original guard or adapting a similar genuine guard, contemporary B and M series pressings are similar, differing in detail, such as extra brackets.
Later plunger models share the non ribbed front guard of the early S/A models. The lower stay is the same, with the two securing nuts and bolts at the rear.
As noted above, Chris Williams at Autocycle, Dudley, West Midlands can be worth a try and knows his stuff from many years in the trade. The range offered includes plain and ribbed blades, but not the deep valanced type, as the original tooling is long gone.
Indian produced ones are a different story, as regards quality and material, but look attractive compared with prices asked for original rusty offerings. When ordering replacements, the size of the guard is not the size of the wheel......we have all made that mistake.
Keep you old guards, either as a pattern or for the future, rusty or not they have a value to someone.
Swarfy.