Actually, black powder 38 S&W is available now for cowboy action shooters.
38 S&W Black Powder Ammo .358" 150 Grain RN Hollow Base Bullet (THIS IS NOT 38 SPECIAL) Box of 50 - Buffalo Arms
That is the problem with countries having laws permitting ownership of revolvers that have no source for ammunition today.. The UK has such laws and as they are reviewed, more and more "legal" arms will become illegal to own. I have sold quite a few Model 3 revolvers to the UK under their obsolete ammo laws, but today almost every caliber has a commercial manufactured source, so what does that mean down the road??