I'm not sure if you can decompile a rule to get its sources. When you are using your rules, you are working with a binary representation of them. The RETE algorithm doesn't know anything about the source code.
Guvnor uses another language to express rules (when you create them using the guided editor), which is BRL. This is an xml representation of a rule. Guvnor maintain the rules in BRL syntax in Jackrabbit repository. When Guvnor compiles your package, the BRL is translated to DRL and then compiled to PKG. But once the rule is compiled you can't go back.
If you have the DRL available, you can use the rule name from the ConsequenceException to search for the source in the DRL. That is all I can imagine. Maybe someone else have a better solution.
Best,