The flat pieces can be made by any decent local glass shop if you have the old ones for templates. They'll usually give you a choice of safety glass like original or tempered.
It's usually cheaper than ordering the ready made sets from the resto houses.
I have purchased glass and fuel tanks from Auto City Classic and have found their products to be of high quality at pretty reasonable prices.
Glass Frames & Channels, Gas Tanks, Power Windows Windshields, Side Glass, Back Glasses All Makes and models from 1930s to 1980s
Auto City Classic, Inc.
28433 Highway 65 NE
Isanti, MN 55040
Orders: (800) 828-2212
Inquiries: (763) 444-5880
http://www.autocityclassic.com/index.php