I presume you have tried GM / Opel dealers? I don't know whether they are still available though without asking the question.
My experience of some dealers is that they sometimes say items are not available, when actually there is stock in warehouses in Europe.
The pipes come in various lengths depending on their position on the car, and come with the relevant connectors.
If you need the part numbers to ask the question of your local dealer, please see the attached link and list of the part numbers of the pipe work.
http://ecat24.com/opel/images/Opel/V94/M/41.jpgGM Name Quantité
9. REAR SUSPENSION LEVELLING DEVICE (CONTD.)
1 1632314 437542 TEE - PIECE,REAR SHOCK ABSORBER LEVELLING CONTROL PRESSURE PIPE 1
2 90473520 437690 PIPE,PRESSURE,1140MM LONG 1
3 90473519 437691 PIPE,PRESSURE,500MM LONG 1
4 90473521 437688 PIPE,PRESSURE,275MM LONG 1
5 90251877 437689 PIPE,PRESSURE,730MM LONG 1
6 90473522 437693 PIPE,PRESSURE,860MM LONG 1
6 90473522 437693 PIPE,PRESSURE,860MM LONG 1
7 90447414 437692 PIPE,PRESSURE,4050MM LONG 1
Hope this helps.