Source for 3/8" styrofoam panels?

[TidewaterVA]

Hello, I am replacing a ceiling panel on a 1995 HR 28' Alumalite 5th wheeler. I have removed a cabinet and the old roof panel, and I need a 4'x8' x 3/8" sheet of styrofoam to replace the original that was damaged. I have checked at Lowe's and Home Depot and can't find it there. Evidently, most of the manufacturers now make only 1/2" and thicker insulation boards. I don't want to use 1/2" as I believe that it will cause a problem with the plastic trim strips between panels that are designed to retain a 3/8" thick board. I have searched online and found the panels at foamboardsource.com, but their product has a paper facing on both sides. I just need a plain styrofoam sheet. If anyone knows of a source that definitely has this styrofoam panel available, I would appreciate the help.

[TidewaterVA]

I think that I have found a source for 3/8" insulation board:
Perma"R" Products, Quality Building Products,

They have 3/8" 4'x8' EPS panels for 2.43 each. They have various sales offices around the US with an order minimum of $25.

[FaithBowls]

Look for a plastics company in your area. My local plastic store has at least 10 kinds of plastics in 4x8 sheets.