Grizzly sells thick blank adapters that can be used to machine your own Set-Tru style backplates.
This. There is nothing magic about a Bison back plate other than it might be prettier than the others. Once your chuck is on it, you won't even notice the difference. I have a Buck back plate that is so pretty I am loathe to machine it but I'm gonna' ...
My understanding is they were a direct copy, just made in China.