The SableCC plugin will generate parsers from grammar files in a certain in your project. By default it will process all files in the src/sablecc directory, and output its results in target/generated-sources. It will also modify the compilation classpath on the fly, to make sure that the target/generated-sources is included in the build.
Note that this means that if you would only move your grammar files in the appropriate directory, then the output of m2 install is a fully self-contained jar file with the entire parser. The cool thing about SableCC is that it provides a clear separation between the parser and whatever you intend to do with it. And with Maven it becomes even easier.