Try leaving your request as a comment to their story at FM.
Even someone who's lost interest in writing transgender fiction,
too busy with real life stuff or any of the other reasons people wander
away from sites like BCTS and Fictionmania (or maybe just don't look
at the message boards) might check every few months to see if their story has got
any new comments. I would be pretty stoked if an author of your standing
(in the small pond of TG fiction anyway) wanted to expand on something
I'd created. Also, I haven't looked to see if this Nay person has
a bio at FM but I lucked out once contacting an author
who had included his addy.

Good luck finding them; I know how frustrating it is to have a great
idea but be ethically constrained to not start on it without permission.
Shakespeare hasn't responded to any of my e-mails and I'm at wits end!
~hugs, Veronica