Nothing is available anywhere, unless you live in a windy area with a lot of active construction. If that is the case, then EPS is available nearly everywhere.
Find an insulation supplier and order what you need. Don't forget about garage door companies. They deal with almost as much sheet insulation as actual insulation companies
When I needed the 3/4" XPS, it still took nearly 3 weeks to arrive and I had to settle for half sheets (24x96). They did have 1.5" available to order (I was considering for my floor), but it had to be purchased by the unit (64 sheets) because it is not commonly used here.