Hi Sophie,
If you want a new part, try
Levois of Colchester.
If they can't help, you could try direct from Japan -
Amayama. You will have to pay VAT on the price and the shipping. The part shown is the actual rack, but it would be an idea to show your garage the parts diagram (Fig 56 in the Parts Catalog) to confirm what is required.
Alternatively, you could get a used complete assembly from a breaker, e.g.
here.