[Hallicrafters] S-38 Series Back and Bottom Material

[vanwagnd at bellsouth.net]

Hello to the List:  What material can be used that is close to (or of course the real thing) the fiberboard like material used in the S38 series for the back or bottom. Most of the receivers I see are either minus those items or they are warped.  I know there is a source out there for replacement backs, but I would like to buy the material itself if possible. Also, anyone had any luck removing the warping and if so, how? 
73
Don