Sulphur melts at about 115 degrees C. Lead melts at 327 degrees C. So one way would be to use a suitable small crucible-like object (like the pourers used for casting lead bullets) floated on top of the melt in a lead melting pot. But hold it in there just long enough to be really fluid - do not overheat, or you will be generating some very unpleasant fumes.
As you can see Joel, you are going to wind up with all the stuff you need to do your own bullet casting and black-powder reloading.
Resign yourself to the fact that all this is going to cost more than the rifle.But...
... for the next rifle, it's already there![]()