where to obtain parts for a roper lawn tractor in uk?

i live in spain and have a roper lawn tractor model no LT120
i am rebuilding the gearbox (soote transaxle model no 4360-7) and need a new key,clutch ( part no 3828 in the roper factory catalogue)
the usa sites don't seem to recognise these part nos and i wonder if there is an agent in uk able to source this part?