So what are you going to do?

Probably purchase some 9.5 and skim.
You seem rather unnecessarily unhelpfull and agrassive in your tone.

The reason I asked is because there may have been some other possibility I
hadn't considered.

Something like: " Oh, in the '70s there was a fad for 11mm board. You can
still get it he www.groovy.plasterboard.far.out.com"

--
Ron