I used to buy all my pork and chicken from a friend who ran a smallholding with a 5 acre wood for the pigs to roam free and root about in, but he's had to give up pig-keeping and the chickens now, so until I find a better (more direct?) source I'm buying from a local farm shop.
Beef comes from a friend's mother who runs a few head of Sussex cattle on her smallholding.
Lamb and sometimes goat comes from a local high-quality butcher. I reckon most lamb is outdoor-reared in UK anyway, but the butcher assures me it's free-range from up on the Ashdown Forest.
Other stuff (venison, rabbit,etc) usually comes from a known source. Maybe not always a source that would be classified as pure, lilywhite and legal, but a source known to me, anyway :-)
I don't eat nearly as much meat as I used to, but do try and ensure that the meat I do eat is from animals that have either been reared humanely or shot from the wild.