About the only two options you have for 7.62x38R is either Hotshot and Fiocchi ammunition, both underloaded (for liability reasons, I'm sure). Both these loads are about in the same ballpark as the .32 Long, according to what I've read. The original Soviet load was, from my understanding, close in ballistic performance to the .32 magnum.
Of course many circumvent the ammunition scarcity by firing .32 long and .32 magnum (which will bulge and stick a bit in the cylinder, but will fire nonetheless).