Line 1158 of the file :https://github.com/Squidly271/community.applications/blob/master/plugins/community.applications.plg Is the issue. It is pointing to the wrong url and giving the 503.
I would share my link to the fork but I am not sure of the rules on the forums for that. Myself and one other member have put in a pull request to make the change. But you can simply fork it yourself. Go to that file in your fork, change the url to read
<URL>https://raw.githubusercontent.com/&github;/master/archive/&name;-&version;-x86_64-1.txz</URL>
Instead of
<URL>https://raw.github.com/&github;/master/archive/&name;-&version;-x86_64-1.txz</URL>