Reproductions of vintage brackets can be had here:
Lake Shore Aluminum Castings
1817 Poplar Street
P.O. Box 59
Erie, PA. 16512- 0059
1-800-458-0463
Inquire about "Windshield Brackets"
If I remember correctly, they are $120+ship per set of 4 pieces: 2 end brackets & a 2pc center section. They are sand castings. Some leave them in a tad rough texture, others grind/hone/polish to a high shine.
IF you are dis-satisfied when the castings arrive, remember that they are individual castings of original vintage hardware that may or may not have been designed to fit your particular boat, so some fitment may be necessary. But if the castings are tweaked or uneven, I do believe they stand behind their products.
Sets pop up on evil-bay every now & then. But at $125, I'd buy the reproductions.
Here's a blog entry w/ pix:
http://tedsbuild.blogspot.com/2010/08/windshield-brackets-arrived.html
and a pix: