Peter Dyson in UKstocks Snider spares, both original and reproduction.. Peter Dyson Gunsmiths, gun repair, gun restoration, antique guns, spare parts for guns
The pivot bar screw and snap cap/protectors are available.. you might struggle to find a breech block though.. remember that the Snider is basically a modified P53 Enfield, so that stock and action spares for these will fit a Snider as well!
Stuff comes in all the time however, and I would drop Peter an Email with what you are looking for.. he and Wendy can keep an eye out for you!