I not any sort of expert on the matter, but I was in the police business back when drop pouches were in common use.....and don't recall a single one that was sized (or marketed) for ".38Spl only".
Look`s kind of like a magazine pouch upside down so the ammo will fall in your hand. I still have one or two but no pictures, we used them in prehistoric times in the 1960`s. They quickly were forgotten when speed loaders come out, and now it`s "what`s speed loaders?" since LE went auto.
I got looking in the garage and found two of them. Sometimes ammo could hang up in them if somehow the leather got pressed or whatever. They do "look" better on the belt than the wider speed loaders that stick out farther. Some had speed strips besides in them.
Galco has or had a model I like. It holds the cartridges two at a time when you drop the flap down so you don't have to fumble with six loose ones. You just pull out two at a time. For a klutz like me it works.