You can get remanufactured ones with polyurethane bushings from Vertex:
http://www.****************************************.com/ShowItem/140883%20Porsche%20Rebuilt%20Lower%20Control%20Arm .aspx
I've got 6k miles on a pair of their rear trailing arms w/poly bushings. So far so good. Cured the terrible rattles in the rear.
Now I've got rattles up front. First I'm going to replace the swaybar drop links, a notorious source of rattles, with these:
http://www.tarett.com/items/boxster~cayman-products/996-986-front-drop-link-set-996fdlnk-detail.htm
If that doesn't do it I'll likely be getting some remanufactured control arms myself.
Let us know how you make out.