Do you have any particular style of sidecar in mind ?
Most sidecar types are still being made today, if you hunt around.
As well as parts to refurbish older ones.
Goulding and Dusting are the 2 names for Oz that came to mind -
-Goulding moved production to the USA, based in their success in the marketplace.
P.S. Its unlikely it was a Norton sidecar ? - they were expensive to buy, as an import.
And most places had local sidecar production that was likely much less expensive, AND stronger for local conditions.