I needed a EC 43R windscreen for my Locost project. So I thought I'd do some research.
I think there are plenty of ways to meet these regulations and if you need more info read this:
http://www.super7thheaven.co.uk/blog/basic-iva-glass-ec43r/
You can use windscreens from any English car from 1976 onwards or any car sold new in America from the 1950's. Any re-manufactured windscreen
should have the right markings.
The side are rear glass should also be marked.
You can get flat glass from Land Rovers Defenders etc.
The above link is a MUST READ!
[Edited on 12/12/18 by seventhheaven]