Head up to the Apple Valley Gun Club this weekend (north end of town, across I-15 from the HoJo Express). They are having their "Mountain Man Experience" 11th to 13th. From their
flyer, it seems they expect some vendors. You might be able to pick up all sorts of stuff.
For your Springfield, you may wish something coarser than FFFg or Pyrodex P (P for pistol). Real black powder is getting hard to find in the stores because of the revised NFPA storage requirements. Luckily, there are several substitutes available. You'll probably be able to get tons of loading info at AVGC this weekend.