Thanks for the suggestions.
Original pictures are on
www.flickr.com/photos/flowtik but for some reason they've ended up miniaturised here.
Rebuilding the brakes would involve fabricating at least one new backing plate from scratch, so if it were simple to buy something similar and weld it into place that would be easier. Given that I need new shoes or resurfaced shoes, the AZUSA option wouldn't be that much more expensive either.
I don't think that straightening the axles is likely to work. We did consider it, but they're straightened, squished, slightly angle-grinded in order to get the wheel off and somehow or another they've already failed so my feeling is that replacement is likely to be better. I could probably fit a larger diameter axle in the wheel using different bearings - which also need replacing.
Thanks for the picture of the FRED wheels - they are the same.