I have a friend with a Winchester Model 1876 chambered in .50-95 which he wants to shoot. The rifle is mechanically sound, but not in a condition to interest a collector, and is a family heirloom which he wouldn't sell, anyway, so there would seem to be no harm in shooting it.

Can anyone point me toward a source of brass, bullets, and dies? And does anyone have any smokeless recipies that are appropriate to this somewhat weak action?

I have decades of experience loading for modern rifles, but this is the first real antique I have attempted, so experienced advice is appreciated.

Stonecreek: Mike Venturino has a section on loading and shooting the .50-95 in a Winchester 76 in his book, "Shooting Lever Guns of the Old West."
Bertram makes brass, and Buffalo Arms (buffaloarms.com) has it as well, probably made from .348. Venturino says that because of the slow twist in the 76, bullets over 330 grains won't stabilize. The factory original was loaded with a 312-grain slug. He used a gas-checked mould from NEI (No. 510-300GC) giving a 314-grain bullet, crimped just over the front driving band to keep it short enough to feed. He shows 80 grains FFg giving 1494 fps.
I would be be extremely leery of using any smokeless loads, even mild ones, in an original 76 because of the weak toggle-link design.
I would call Dave Gullo at Buffalo Arms and ask fopr advice. If you can somehow use .50-70 dies (under $30 from Lyman, etc) to reload this round, your friend could be shooting his old thumper at reasonable cost. A set of proper CH-4D dies runs $120, though.

Stonecreek,go to the Accurate Powder web site and ask about loads with XMP-5744,it seems to work real well with the old black powder stuff,and the guys and gals at Buffaloe are great to deal with.