Ithaca Double Trap
 

The single trigger has stopped working properly. You can fire either barrel but it will not re-set to fire the second barrel after the first shot. The selector is the safety type. I do not know much about these. Wold this be as simple as a broken spring?

Early on, Ithaca Gun Co. used the Miller Single Selective Trigger on their NIDs. The list price was $30 from 1926 to 1932. For 1933 it went up to $32.45. Then Ithaca's designer Harry Howland got a Patent to get around the Miller brother's and by 1934, Ithaca Gun Co. was doing their single selective triggers in-house and the price dropped to $21.60 where it stayed thru 1939. Probably best to contact these folks --

http://www.millersingletrigger.com/services.html

or

Gunter Pfrommer in Rocky Mount, Virginia.