I found an insulation supplier here in central Virginia that sold all kinds of stuff. My 2" eps was $30 a sheet. It looked like they sold to builders and the like. No minimum number of pieces. Maybe something like that around your parts?
look for foundation installers, that is what XPS is mostly used for, to protect concrete from cracking where rocks in the backfill would put a stress on one point in the concrete. If they don't have any, they should be able to pass along who their supplier is. I get the same issue with people who want to build my Sawfish kayak.
Found some! but had to do some digging. Lucky for me since they place I got it from doesn't sell 3/4" that often that had a lot of waste/broken pieces I was able to take off their hands for free
Started gluing up the floor today. Been going back an forth between using PL 300 foambond or the PL Premium, ended up using PLP for now