Try looking at
Motorsport World - Performance Car Parts
They sell H&R Stuff (I bought my H&R Cayman S - Anti Roll Bars from them)
They are very helpful - if you do not see what you want on their listings - TELEPHONE THEM - They will get the exact stuff you want over from Germany........
You need part number 29168-1 Porsche Cayman + Cayman S Typ 987
color black, lowering [mm] 35, year: ab: 11.2005 from the H&R Germany Website
H&R Spezialfedern GmbH + Co. KG
What is more they are Scottish!