You can get 32acp bullets in .312 diameter. You would probably have to load your own using .312 *lead* bullets though. Standard 32acp rounds are jacketed, and wouldn't be good for the forcing cone and barrel on the little remy, same thing for the bigger Colt and Remington reproduction revolvers (lead bullets only).
Secondary thoughts:
1) By the time you get the .31 remy, and .32acp cylinder (considering the cylinder would cost about the same as a .31 S&W conversion cylinder), you could have gotten something designed for 32acp that's better, smaller, lighter, and cheaper.
2) 32acp is semi rimless, so it has a bit of a rim. I can shoot 32acp in my revolver made for 32 S&W Long, and it will go bang, however the pressures for standard 32acp is higher than the 32 S&WL. My 32 S&WL revolver is made for higher pressures and can take the abuse, though, I rarely do it (I reload 32 S&WL anyway). I wouldn't shoot 32acp in a 32 S&W (short) gun. Not saying that the gun will explode in your hands (however it could), you will ruin the gun fairly quickly if you practice a lot with it (as you should with any self defense gun you carry).
