http://blogs.adobe.com/creativecloud/dpsse/
It can be clunky in places and I've seen terrible magazine apps created with it, but that can be said for native apps as well. There is the Adobe creative cloud price to factor in, but if you are doing anything with creative cloud already, you have access to this.
As for actually getting into the actual iOS newsstand as a magazine, that I'm not clear about. I have the impression that Apple has tight relationships with legacy magazine publishers and gives them priority.