We used to get cork in 1M X 1M sheets for making rocker cover gaskets for the engines in the Old Katherine Power Station. I think It came from Blackwoods .I think it was up to 1/4" in thickness.
Not sure if it is still available ,like the engines probably long gone.
What we didn't use for gaskets we used to line the bottom of our tool box drawers .
In fact the big 9 drawer tool box in my shed still has the cork mats in the drawer bottoms .
Kev