I usually make something similar to the penny washers by cutting squares out of scrap steel about 1 - 2 inch square, drilling a hole in the centre and turning up the corners so they grip what's left of the heat shield.
Not sure what the fasteners are, but if they are the push-on starlock type fasteners, you can get replacements for these. If the studs are too corroded, you may have to resort to improvising some other method of fixing.