as I said, I don't know how. Low velocity loads are hard to achieve. Even the old .38 S&W is in the 700 fps range with 158 grain and larger bullets.
The problem is the combustion chamber size.
Again, going back to old school techniques, a writer experimented with cutting off .38 special brass, thus reducing the combustion chamber to a minimal size, then loading standard bullets over bare minimal charges.
The .38 short colt is in the 700 fps range, and I believe that it can be fired in .38 special handguns. It maybe can be downloaded to 500
You can, very easily, find .38 short colt ammunition and brass.