He's on ebay ...
Here's a link to the speakers.
http://cgi.ebay.com/ebaymotors/Porsche-Boxster-Rear-Speaker-Kit-1997-2008-Upgrade-/220691578423?pt=Motors_Car_Truck_Parts_Accessories&hash=item33623e3e37
(I ordered the door sills from him. They are pretty good quality and fit nicely)
I actually just did my own rear speakers for less that $100 (polk speakers + all materials). I can post the installation pictures if people want. I also created a template to cut out the speaker mounting boards.