Hi Purna,
The repository is at https://github.com/hibernate/hibernate-tools
https://help.github.com/articles/fork-a-repo explains how you fork a repository and https://help.github.com/articles/be-social shows how to create Pull request.
The code is plain Maven project you can import into Eclipse with m2e installed or some other IDE that understands maven.
You can build the project by running "mvn clean install -DskipTest" (of course remove the -DskipTest to run the unit tests)
You can probably add a test into https://github.com/hibernate/hibernate-tools/blob/master/src/test/org/hibernate/tool/hbm2x/Hbm2JavaTest.java that tests your case.
Welcome to being able to contribute - we are also in #jbosstools on irc if looking for help, but if not finding it there just post here.