You know, I've spent hours strolling through Lowes looking for materials for this type of thing.
The one near me actually sells Blue Styrofoam Insulation in 2" thickness in a 4'x8' sheet. My problem with it is twofold:
1) getting the darned thing home
2) All the pieces they have are gouged in some way or another that I don't feel like dealing with.
I've walked through the door section to see what was there but I didn't notice the doors you speak of. However, now that I have the name, I'll be able to focus my search.
Thanks for the tip! Have a gold star