Guess I missed this thread.
We have "Foam Factory, Inc." - which is a short drive from us, but is also a big online store. They have every kind of foam imaginable in different densities. Might be able to ask for samples.
I wouldn't dismiss cutting up a replacement sponge meant for kitchen mops, you can find in any grocery store. A repositionable 3M Adhesive Spray can be found at Office Supply stores or any place crafts are sold.
Art Supply & Craft Stores carry material - even dry flower arranging foam is light & easily cut to shape.
Dr.Scholl's carries a thinner adhesive-backed piece of foam you can cut to size, Mole Foam - also found at most Drug Stores.
Keep in mind any foam, other than the Dr,Scholl's, might work better with a cloth covering.
Btw, I don't spray ANYTHING in the house unless you can spray within a large cardboard box - even then, you'd be surprised where overspray settles.