Both IT Supplies and B&H seem to have figured this out and I haven't had a problem with damaged paper with either for the last couple of years.
A few years ago, I ordered a bunch of sintra board, I think 30x40. After the second box arrived mangled like the first I had to return and they offered me a discount if I'd take it, it all went back. I stopped buying from that vendor because they never could keep the board from damage. In the mean time I was lucky to find a local supplier for that project.
Getting boxes of paper delivered in a properly-packaged box is priceless and though it probably costs more, it's worth getting it undamaged quickly from a few chosen vendors rather than going for the cheapest price.
In any case, it may be worthwhile to call around and find out which warehouse (there are dozens all over the country!) and find out if it's the closest to you to give the shipper fewer opportunities to mangle the boxes.