^ Yes I can understand because Im have experienced that how difficult it is to find parts for a 99 model Khyber.
Anyways I think that you should consult a good shock wala.
Cultus springs donot sound a good option to me.
Consult any good shock wala in your area about Corolla,s springs.
They have springs/pumps of almost all the sizes.
Moreover they can be custom made by alteration of bigger sized springs.
If you are in Rwp then I can tell you about a shop in Saddar.