A survey done by AFB in the 1990's stated that there was a demand and a shortage. You might wish to contact AFB or NFB or NLS to inquire if there is any current research being done. Because of the various code certifications Math and Music transcribers are probably lower in numbers than literary transcribers, however that is my opinion and I have no numbers to back me up.
I am interested in either completing certification for Nemeth Braille or brailling literary braille for someone or organization. I've been certified in literary braille for a number of years, maybe 20? Thank you for any information available. I did note the suggested organizations to contact for literary braille, but the comments sounded like just research questions.