Over here you can get sliced pieces of foam rubber at those large DIY-supply stores and at workshops specialized in custom-cut foam for upholstery etc. You also can get that sound absorbtion foam with conical surface strucrture and even that cubicle-cut foam. I assume the supply situation is the same in Poland.

But restoring the kit would only make sense if you want to re-gain the original state or even improve it for carrying around.