With such a small, light airframe,have you considered bicycle brakes?
Both disc and drum are used and operation is cable, (as you already have) hydraulic or rod.
Inch bar seems quite small for a cantilever axle Maybe it's just had a heavy landing or two,maybe with wrong tyre pressures. I think it unlikely the axle would be welded to the gear-leg and then the whole shebang hardened and tempered....more probably it's just a lump of bar of the correct grade, turned as needed and welded-on.
You seem to be at the bottom of a steep learning-curve here.AIUI, you are expected to come up with the ideas for a fix or mod and then submit it to LAA engineering for approval. that is, they don't do the ground-workfor you......so,that leaves owner's associations, other Permit flyers , friendly engineers/mechanics or paid engineers.
You could sit downwitha load of textbooksand a calculator and workout what spec.of material is needed etc......but my gut feeling is that , from what is already there, you should get a good idea of what would be suitable.
You may also find the importers of small "quadbikes" and mini-motorcycles may well list drums/backplates/shoes etc. which can be modified.
There are plenty of firms who will reline bonded brake-shoes or supply lining-material/rivets todoyour own. Have you looked at the possibility of straightening the axle(s) ? Cracking is not likely to be an issue, many firms specialise in straightening motorcycle forks and frames.
Unfortunately your pix are too small to see a great deal.
HTH.