There's also ao3feed-stevetony.tumblr.com (http://ao3feed-stevetony.tumblr.com), which posts links to all the stony fics being published on AO3 - that's a good way to find authors and their tumblrs (a LOT of authors have a little "hi, come find me on tumblr" blurb in the notes at the end of their fics)
If you can use the 'find new blogs' function, that will help you search for tumblrs without using tags - the recommendations are based off your likes and reblogs and who you're already following, so often there's cool stuff there. And definitely check out people's 'following' lists on their tumblrs, it's a great way to find less obvious blogs - I found shawarmababy.tumblr.com (http://shawarmababy.tumblr.com) that way, and that blog has a fantastic Stony fic rec list, for instance.
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If you can use the 'find new blogs' function, that will help you search for tumblrs without using tags - the recommendations are based off your likes and reblogs and who you're already following, so often there's cool stuff there. And definitely check out people's 'following' lists on their tumblrs, it's a great way to find less obvious blogs - I found shawarmababy.tumblr.com (http://shawarmababy.tumblr.com) that way, and that blog has a fantastic Stony fic rec list, for instance.