Hi Chairman Pill, I am on the border of south oxfordshire (Caversham) which used to be in oxfordshire once upon a time.
Although I am not a proper small holder (in my eyes) I do try to grow lots of veggies in the garden, when I have the space I would love to get some chickens.
I am sure there must be an association of sorts but maybe they don't cover the whole county, I have tried to look for associations in Berkshire but to no avail.
Maybe if you contacted the local allotment association to see if any of their member know of anything, it might be a good place to start?..