Don't think that is what he is looking for.
If you are handy w/a bandsaw or just a jigsaw a counter bore,dril & tap,, you could buy 1/2" alum plate & make it yourself.
Or buy from Offy or possibly Langdon? here is a pic of the adaptor you need.
http://stoveboltengineco.com/index.php/c...product=1222035MBHD