There is no download for AS7.3, this is discussed in several thread in the forum.
You might build the AS based on the github repository from a 7.x tag.
But I recommend to use wildfly as this is the current upstream version
As per Wolf-Dieter is correct one. If you need JBoss 7.1.3 you can try this link. It is good. I am also using JBoss which was downloaded from http://blog.kaltepoth.de/posts/2013/02/12/building-jboss-as7.html