Some building supply stores have it. Menards, Lowes, Home Depot. About the thickest they have is 2". Another source worth looking into is commercial builders. Some use thick billets of foam as the outside decoration on stores, condos, etc. They stucco over it and then paint it. That's where I found my last chunks--2'x1'x4'. A local restaurant was up-dating its front and the builder used foam and I got some leftover pieces. Regards.