Here is an older thread that I believe discusses them:
http://986forum.com/forums/performance-technical-chat/16061-any-one-used-all-ches-suspension-pcs.html
Do you need them for the front or back?
For the back you can use the TRW Arms:
https://www.amazon.com/TRW-Automotive-JTC1186-Premium-Control/dp/B00T9YHFCE/ref=sr_1_2?s=automotive&ie=UTF8&qid=1468421799&vehicle=2000-2-18-87--8-6-7-1140-40-1-1---1-0&sr=1-2&ymm=2000%3Aporsche%3Aboxster
For the fronts you can use these: 99733104301
https://www.fcpeuro.com/products/clone-porsche-suspension-control-arm-911-37143017001
I am running this part number on my 2000 and can confirm it is an exact match (and if you look on the Meyle website you can see they list the 986 as a match - unsure why other sites haven't picked that up. I think that is why you can't find the 986 TRW front arms any more, because TRW also makes the 997 arm which fits)