Mike, thank you for your welcome,
As always in Germany, it gets complicated when guns are involved.
I try to explain the situation briefly.
Concerning the powder:
The availability of black powder is good. Percussion caps are on shortage as everywhere.
To purchase powder you need a permit. Permits are given to members of gun or reenactment clubs only.
Concerning the guns:
Guns with spark ignition (match lock, wheel lock, flintlock) are free for adults, no matter if double or single barreled.
Guns with percussion locks are free as long as they are single barreled. Double barrel caplock guns or revolvers are restricted to holders of a special permit.
Christian