You can a make glare-shield out of fiberglass fairly easily if you are careful.
I will relate what I did to make the upper interior cabin panel in my F, now transformed to mostly a J with Ovation interior.
Since it is highly modified I had to modify or make interior parts. One such part is the upper interior panel of the cabin door. My F model door has been reskinned, and fitted with a rounded Ovation-style window, but is not as tall as the Ovation window. Also the compound curvature needed to be changed to fit the door and interior.
After many trys of hand layups, I decided to use the pane itself as my mold. I fractured the fiberglass panel so it could be screwed in place on the door.
I covered the door and exposed airplane parts with clear vinyl wrap, then screwed the now flexible fiberglass panel in place. Being careful to keep things clean, I hand layed-up layers of fiberglass to make the panel as guided by the panel which was screwed in place. When dried, the panel was worked as needed. You can either use cheap boat yard grade fiberglass, then when the part is finished, use is as a mold to make a fire-proof version, or use fire-proof resin initially.
You can place linear supports, use duct tape, or whatever is necessary to support the lay-up part until it dries. Protect avionics, seats, upholstery, etc. with sran wrap or similar. Fabric stores have rolls of plastic wrap of various thicknesses. Use your manual skills and creativity and you can get exactly what you want.
John Breda