Try Mountain View Auto Interiors:
1900 Old Middlefield Wy B
Mountain View, CA 94040
(650) 964-8096
mountainviewautointeriors@gmail.com
Bob Demarco (the owner) gave me a killer price on installing my glass top and on covering a seat in leather
Bob has done over 100+ Boxster glass tops do far, so he's very familiar with the Boxster top and I am sure he will give you a great deal on putting a new plastic window in