List based on calling, not member name?

I have a list of all Sunday School teachers to send them all messages from time to time. When people are released or called, I have to manually update the list.

I’d like to have a way to send to all Sunday School teachers without maintaining a list of member names. The app could simply send or build a list based on the calling “Sunday School Teacher.”

Is this possible already? If so, how can it be done?

I don't think that is possible.
Unfortunately the new send a message feature in [LCR] -->[Applications] only has Presidencies, Ward counsel and such in the choose lists and not teachers.
In order to use that you would have to maintain your own list of names and then choose from a list of all adult members in the send a message menu. At least you would not have to maintain the email addresses that way...... assuming the the members email info is up to date on their record.