others I've seen

Worldwide Club & Festival map by Chris Rust 
www.google.com/maps/d/viewer?mid=zFcKphOvGxXU.kaygq-TxL-oI&z=8&ll=52.8%2C-2.1  
(if it gives you the option, open it in the browser, not 'maps')
You'll need to change the layer displayed from clubs to festivals.

+ info about it
https://folkmusicmap.wordpress.com/about-2/  


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Living Tradition - Festivals List
/www.livingtradition.co.uk


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  Mudcat's Mr Red's  ... focused on the southwest but I bet it's bang up to date          
http://mister.red/fest.html