try gunstock inc. they have them
In reproduction catalogs from Sears @ turn of the century
The front trigger opened the breach.
The back one is for the left hand barrel and the front is for the right hand barrel.
A good place to try is gunbroker.com
CountryGunsmith@direcway.com has everything you need.
I have two 1878 Jas Parker & Sons double barrel shotguns.