Might be a bit late with info but only just joined forum. Al-Ko shock absorbers are only available from Al-Ko.
You need to contact Outdoor Bits,ask for Ben or David ,tel no 08458698940 who are very helpful.
Don't be tempted to fit Al-Ko shocks from a caravan,these are a totally different type.
Shocks are colour coded,the will know which type you need.
Expect to pay £103 for each shock,only fit in pairs,plus postage. They take around two weeks
for delivery.
Service is good.