I've just heard back from the garage, and apparently they have managed to find the Rear-left and rear-right cables.

They found out from cross referencing the old Alfa part number that they are shared with the Dedra Integrale, thats Dedra not Delta, and also a Fiat Tempra. They are winging their way to the garage now, so when they arrive, and IF they fit I'll get the details of them and let you all know where they came from.

Fingers crosses.