I just bought a rolls of the insulation. The stuff in the back I bought from
www.tld-corvette.com for under $30.
The shiny stuff is called Reflectix and I bought that from Lowes for about the same.
I liked the Refelctix better because it is thinner and easier to work with. I didn't find out about it until after I had completed the back.
No idea where to get them. Try the junkyards. I think I have a couple listed under vendors on my site.
Bob