Hi, first don't take the green house down, just remove the glass, you can then cover this in Chicken wire and a roof of some kind and you have a walk in run for your hens, all you need then is a house inside this. (not my idea visited a farm a few weeks back and the old boy had several broody coop like this).
We are actually not to far from you, as we are in West Yorkshire.
We have 5 Bantams and 5 Ducks at the moment but intend to increase this in the near future. We are fairly new to poultry keeping ourselves having only had the Bantams for 3 months.
As for where to get them if you get hold of a copy of Practical Poultry there are plenty of breeders in there, if not have a look at your local papers for adverts or pay a visti to Selby Livestock Auction (Alternate Saturdays, there was one last week, so the next isnot this saturday, but the week after).
Hope this helps.