Firewall insulation sources

[wbmoore]

My 1982 C/30 DIESEL Silverado came with hard insulation panels on the firewall outer surface. In the process of swapping the 6.2L diesel out for a Cummins 12V, some of the hard insulation has deteriorated through damage and age.

Does anyone know if or where replacement panels of this type can be purchased ? The panels cover the A/C unit and the complete firewall. I would be interested in new or even used if undamaged.

Thanks. Happy Holidays.