Well casing should work very well, and 10 inches is a good size. After you line it with one inch of inswool, it leaves you an 8 inch hot zone.
Fire brick - the soft stuff - can frequently be found locally.
The Satanite and Inswool MIGHT be found locally - depending on where you live! Most generally in a large metro area.
Otherwise, there's plenty of places to get them on-line.