Here is Yahoo! Directory on selective mutism.
Directory > Health > Diseases and Conditions > Selective Mutism
But there is no directory about selective mutism on Yahoo!Japan.
At present two Japanese websites about selective mutism are listed on Yahoo!Japan.
The one is in the anxiety disorder directory.
The other is in the handicapped children directory.
Yahoo!Japan have a dominating presence among Japanese search engine sites. Japanese people use Yahoo!Japan search rather than Google search. So, it's important for Japanese web masters whether their web sites are listed on Yahoo!Japan directory or not.
I also manage a Japanese website The Selective Mutism Journal. I tried to submit my websie to Yahoo!Japan several times, but my website has never been submitted. :(
Index of SM in Japan