I have two sheets of plywood that may be of use to someone
They are both 5 or 6mm ply (depending on which tape measure I use!!)
One is 620 x 880 mm
The other is 680 x 715 mm
They have posters pasted to the reverse side which could be stripped so only one side is clean as they stand
X2 sheets of 5mm plywood (Wolsingham DL13)
This offer has been gifted to someone and is no longer available.