I was looking through the London Drinker. That is one great magazine; it's the mag of the London Branch of Camra and it is given away free in a lot of real ale pubs.
It has adverts for beer festivals all over Britain, and the current one has an advert for the Isle of Wight Beer and Buses Festival.
That is held on the weekend of 14th & 15th October 2017. The vintage buses are free to travel on, although they prefer it if you have a program. I have indeed bought the program and it is £6.
There is a list of the beers here:
Many of them are not unusual at all. Fuller's London Pride won't be on my URGENT list, nor Timothy Taylor Landlord. I've had plenty of them. I'll be trying Yates's On The Buses, though, among others.
I'll be staying at Sandown, and the Castle has the following selection of beers:
Scary Man Trick or Treat
Black Annis Porter
Trooper Red & Black
Green hopped IPA
Bombardier Burning Gold
Bombardier Glorious English