You could do with a network of geographically diverse contributors, Conrad, and an easy way for them to enter festival data (pending moderation) from local Camra magazines or direct pub knowledge. I'd happily do it from London Drinker, though I'm not in my usual 'circulation' at the moment, but from the most recent online version the only missing dates I noticed were 21-25Jul at Pembury Tavern
http://www.pubsgalore.co.uk/pubs/25070/. A pal occasionally mails me Opening Times (Stockport/South Manchester) so I'll keep a weather eye on that if/when it arrives.
Anyone else have local mags? I recall being asked whether I had a beer belly in Rochester (it was quite evident I did!) but, to the locals amusement, & my own, it turned out the barmaid was referring to Rochester Beer Belly, the local ale mag. So... there must be plenty of Aylesbury Ales, Dudley Drinkers, Brummy Beers, Salopian Suppings, Dartford Dipsos, Lancashire on the Lash, and Yorkshire Guzzlers out there.
I imagine you could get a list from Camra and the local branches would probably send free copies if they knew their festivals (pub or independent) were gaining exposure.