This is an area that I know nothing about, however, recently I was
writing a script to change the pitch of iTunes pieces so that
students could play their instruments in normal tuning and I was
given some UNICODE that contains the double flat in it. You might
like to see if you can get the code from that. I'm sorry, but I
can not remember who on the list gave me this part of my solution.
set shift_list to characters of ¬
(«data utxtD834DD2B266D266E266FD834DD2A» as Unicode text)
set shift_value to choose from list shift_list with prompt ¬
"Choose a pitch shift:" default items shift_list's middle item