I knew you’d want chapter and verse!
I have used a couple of National suppliers with good results. The price varies a bit against the exchange rate of the dollar and other factors.
What I do is to buy a selection of timber, mostly American White Oak, American Cherry (outrageously expensive!) plus cedar for drawers etc about once or twice a year.
It will come sawn in random lengths, usually 3 m plus.
I then run a wire brush and a metal detector over it (Some trees have bullets in) and thickness it. It then gets sticked up until I want to use it.
Buy the thickness you need and don’t be tempted to re-saw. It will twist like mad.
Try these, you’ll have to ring up for a price and be prepared to convert to cubic feet if that’s your language.
Timbmet in Oxford
http://www.timbmet.co.uk/
Plus Arnold Laver’s world of wood. All over the place.
http://www.laver.co.uk/
I’ve not used SL, but they sound OK. They are in south London somewhere.
http://www.slhardwoods.co.uk/
You may have to add VAT and transport costs.
You get what you pay for. And quality is never cheap. I have used decent English oak in the past but it's a hedgerow tree these days and the quality is variable, not to mention the MC.
The Yanks are consistent in quality in the drying department.
Hope it helps