Welcome to iboats Tul!
Yah, if she is 18' probably a Starchief.
To be quite honest, you are going to have a real tough time finding that stuff. I'd think your best bet is to hang around here, in the iboats restoration section, or in the Starcraft section, in an effort to find a guy who is tearing the lid off of his Chief or something. Rare, big time.
Or, find a company that can custom build the framework for you. That'll be kinda pricy though.
The thing about these ol Starcraft cabin boats is they have that track that your windshield will slide into so it has to be specifically designed for that.
But, probably a third option could be...
Drill out that track all together and find a good fitting replacement windshield from a donor boat or something.
I dunno, just thinking out loud here.
Got any photos of what you are working on
Cheers