I, too, just had a total joint replacement. I asked my oral surgeon for one. They do have a website; but, I don't think you can order it from it.
I had one about 12 years ago after my open joint. It helped tremendously. Stupid for me., though, I threw it out..because the surgery worked.
I find it helping me now, though it is kind of expensive. But, as road8 said...the tounge depressers work too. and, they are not expensive