I read the OP requested holster info on J frame revolvers so I decided to post what I bought last year. A Friend used to be a Deputy Sheriff in rural midwest in the mid 70’s. He was issued a tapered barrel model 10 but carried a 3” model 36 off duty or in plain clothes. He sold the model 36 and shoulder holster to another Friend. Knowing both guys I couldn’t resist when I had the opportunity to buy the model 36.
Shoulder holsters were kind of common in the 70’s with small revolvers. I never really cared for Shoulder holsters even though I used one occasionally. Colt Detective Specials (Agents & Cobras) were popular as well as the various S&W J frames in the 60’s & 70’s. The most common holster I saw officers use with small revolvers back then were simple leather belt holsters usually with a safety strap. I also observed a few clam shell holsters where the spring clip inside the holster body held the revolver usually with no safety strap. This clam shell holster was commonly carried at 10 O clock sort of cross draw. I knew an Indiana State Police Detective who carried a well worn Colt Cobra revolver in plain clothes. This Detective did not use a holster but had rubber bands wrapped around the top of the grip so the revolver would ride inside his waist band.
The Bianchi shoulder holster pictured below uses the same type of spring clip with no safety strap as the clam shell belt holster I previously described.
The only person I observed carry a J Frame or small Colt revolver in Uniform was a female Deputy who worked in the Jail. The female Deputy would assist Road Deputies any time a Female Deputy was needed for arrest, searches, or mental cases. This Female Deputy carried a J frame 3” or 4” revolver in a basketweave leather holster with basketweave duty belt in uniform.
It was not unusual for an Officer not to carry extra ammo on his person for his small revolver in plain clothes. I was kind of the exception as I usually had at least one speed strip for my model 60. Speed loaders were fairly new in the mid 70’s and not commonly encountered for small revolvers.
Here are pictures of the 3” model 36 and shoulder holster even though I replaced the factory grips with Pachmayr gripper grips (I still have the wood grips).