hello,,may be a hard item to find ,,a gunsmithe may be able to duplicat it if you have one thats broke,,or someone who makes custom wood should be able to help you but either way i don't think it's gonna come cheap..gunparts have parts for your shotgun but don't have stocks listed ,,
http://www.e-gunparts.com/products.asp?
chrMasterModel=0660z1878%20HAMMER%20DOUBLE%20BARREL&
MC=
bigcurt