You can get EAP 6.1.0 which is the hardened version of JBoss AS 7.2.0. This should be free to use as a developer. That would be my first recommendation. (Snowdrop is designed for EAP, which is based on JBoss AS.)
If you want the plain old JBoss AS then you will need to go to github and build it based on the 'tag' of the version you are looking for.
JBoss AS 7.1.2
JBoss AS 7.1.3
JBoss AS 7.2.0