I managed to find a used 4D0599133(D) bracket on Ebay (the only one in the country it seems), which was a relief because the bolt was seized into the old one I'm told, making it impossible to re-use. I'm not entirely sure it's exactly the same part (possible a different suffix letter) but it was cheap and I figured we might be able to use the bush even if the bracket turns out to be the wrong shape.
The bushes on the other bracket (4D0599285) are a bit knackered I think but probably still usable so it shouldn't stop the garage from putting the car back together.
After I gave up looking for the brackets I started looking for bush manufacturers/suppliers and found this place, which is fairly local to me (about 20miles away):
https://www.fibet.co.uk/
So I emailed them this afternoon about supplying one-off bushes for vehicle suspension parts and, to my surprise, their initial reply is favourable, stating that they "
don’t have a minimum order quantity just a carriage charge of £11 + VAT for order values below £150". I'm planning to contact them again tomorrow to see if I can maybe arrange to call in with the parts.
Edited to add:
I wonder if any D3 parts would fit the D2 ...
The 4D0599285 bracket, for example, seems to have a D3 counterpart that's just one letter different (4
E0599285). And, physically, the D3 part appears to be quite similar, with holes in all the right places (see attached images).