right help at hand!!
this is very easy.... 1st obviously they were made for your vw, so thats that!
2nd spax only make 3 types of strut!
1 the vsx kit, normal fixed damper! same as standard shocks! but harder of course!
2 top ajustable psx kit, this is so you can adjust the hard and soft level!
3 coil overs rsx kit, but they look different so it wont be them!!
so its either a top adjustable or the normal fixed shocks! it should be easy to tell if they are top adjustable as they are yellow.... the non adjustable are black in colour!!
you should also have a sticker on them saying what kit you have! also you should have a number stamped on them somewhere!! to say what type it is! etc
any dealer who sells spaxs can order them.... but they will only send a pair!
our apex front shock went one side went funny leaking oil!
so we told motor world and they rung the supplier and they sent 2 new shocks......!
you should be able to order them!

heres a site which sells them prices are for individual shocks so dubble the price if you want a pair!
http://www.motorsportworld.co.uk/frame-detail.asp?PAGE=/manranges.asp

i hope this helps