I've seen a build where a guy was sandwiching mineral wool between steel panels to insulate his Q. I thought this was a great idea to prevent heat bleed off. Mineral wool is rated up to 1200 deg C and much better than fiberglass.
Ceramic Fiber board is not easy to find and when you do, it will be a lot more expensive than mineral wool. If you're still stuck on ceramic wool or fibre board you should be able to get it from an idustrial product supplier. Hope this helps with your build. Make sure you document your build and keep us posted on your progress thru pics!