Coffin arms - use this Meyle part, the price fluctuates but I got them for <$100 each with free shipping, ECS often has this one on sale for <$100 as well. I think I got them for $86, I am running these on the back right now, been very happy with them so far.
https://www.fcpeuro.com/products/porsche-control-arm-rear-lower-911-boxster-cayman-4160500000
Rear track arms - TRW from Amazon:
https://www.amazon.com/TRW-Automotive-JTC1186-Premium-Control/dp/B00T9YHFCE/ref=sr_1_1?s=automotive&ie=UTF8&qid=1471016083&vehicle=2000-2-18-87--8-6-7-1140-40-1-1---1-0&sr=1-1&ymm=2000%3Aporsche%3Aboxster
Front caster control/track arms - this is the right part, it is the rear track arm from a 997 - I believe this is why the TRW version for the Boxster Front and 996 all 4 corners is so hard to find, it has been superseded by this part, and the cross references haven't picked it up. I am running this on my car right now, it is an exact match, if you look it up on the Meyle website is shows this part as fitting 986 front, 996 all 4 corners, 997 rear.
https://www.fcpeuro.com/products/clone-porsche-suspension-control-arm-911-37143017001
I ordered this part and what came was the TRW version, no complaints from me
TRW and I believe Meyle also have the tie rods, and anti-roll bar drop links are another creaky part that might be worth replacing if you are doing a complete refresh.
For most of these parts, TRW makes the Porsche part and if you buy TRW you get the exact same part with the Porsche marking ground off.