It is a handloading proposition.
Once upon a time, Armscor imported some .22 LR primed empties, but now the only option is to pull bullets and discard the nitro.
It is a tedious process.
Dies have been made and/or improvised.
Best to cast fresh bullets, pulling a crimped heel bullet doesn't leave much.
Fouling from 5 grains of powder is not a huge problem.
One of the guys working on BP .22 showed a target shot after 50+ rounds without cleaning. It was a bit over an inch at 50 yards, which he said is about what his Marlin 39A will do with smokeless.