Insulation

I know this may be a bit off-topic, but I need some help. I am building a
thermoforming oven, and need to find a suitable insulating material. The
oven shouldn't reach over 500 degrees. Most ovens used for this application
use 1" Rockwool insulation, but I can't find any. Does anyone know where I
can find some or a suitable replacement?

Thanks in advance,
Jeff Pietrowicz