I inquired about a new(old) backglass from Mayfair in late May of this year and here is his response. Hopefully he won't mind me posting this.
I have a quality reproduction Black Knight backglass that was made by Williams in 1996. It is just like the original in form and fit, and printed on glass not plastic. They upgraded the quality of the ink to address the issue of peeling on the original 1980 run. All colors including the mirroring are exactly like the original. It is simply perfect! I have sold dozens of these and never had a problem from a customer. The price on the glass is $275, add $45 for a trim package that includes a new stainless steel lift channel and plastic outside edge trim. Shipping is $75 East of Chicago, $95 West of Chicago in the USA. All backglasses are sent UPS fully insured. For International shipping ask for a quote. If using paypal add $20 for fees. If sending a US Postal Money order, no additional fees
I have his contact info and can send in a pm, I don't want to post in a public forum.