Check out Frank Allen’s webpage, and contact him directly
if you have any questions. He teaches at the Healing Tao Retreats
every year, and is our resident expert on all things
having to do with Bagua and Xingyiquan.
Teachers I know with great knowledge on this would be Shou Yu Liang, Sam Masich, Henry Look (was a student of Han Xingyuen), students of Kuo Lien Ying. The problem you might run into is that once you begin asking about specialized skills within a lineage, many teachers will clam up. Especially if you are not Asian, as open as things are getting there still many who don’t like to share.