I get a lot of my wood from Hoyle Hardwoods in Llangernyw (01745 860376). Dave almost always has what I need in stock and it is usually from the UK.
The wood is sawn using a giant band saw powered by a bus engine. It is then stacked for months or years (depending on thickness) to air dry and then kiln dried to lower the moisture content further. Local ash and oak usually have more interesting grain figure than the imported varieties you get from the builders yards.
Woods like elm, sycamore, yew, cherry, sweet chestnut, lacewood and beech are all available, although some intermittently which makes them feel a bit more precious. A wide, sound plank of yew is a rare thing and given that the tree may have grown for over a thousand years is something to be used carefully and with respect!
Sometimes I get wood direct from the Gwydir or Coed y Brenin forests, planked in the woods with a Wood-Mizer portable saw mill. There is an abundance of larch and Douglas fir which are perfect for building projects and outdoor applications due to their high rot resistance.
For sheet materials - when making a kitchen cabinet for example - I use red pine board or birch ply which, as well as being nice looking are a bit more planet-friendly than far eastern rainforest ply. Both birch and pine grow relatively quickly in well managed forests in the northern hemisphere.