There's a shop in Corvallis, OR named "The Foam Man" that has been in business for something like 30 years. They sell everything foam. They will cut it to any size you ask. Prices are very reasonable. I have purchased foam there for audio, for shipping, for sleeping, for my pickup, and for my parents. It's a cool place to walk around in and have all kinds of neat ideas and projects come to mind.
Give them a try.
(541) 754-9378
Michael