Answered my own question from their web site:
"Where do you ship?
We ship Amazoy plugs throughout the continental United States with the exception of Washington and Oregon. Our experience shows that weather conditions there generally are not conducive to the successful growth of zoysia. Unfortunately, we are unable to ship our product outside the continental United States (we cannot ship to Alaska, Hawaii, Puerto Rico or Canada)."
I guess it isn't banned - it just doesn't grow here.