Whilst camping in the Cotswold's a few of my fellow campers were enquiring about the green & very warm (ex) military shirts I had with me. I promised to post details ....
This is where I got mine from: http://www.anchorsupplies.com/clothing/shirts/norwegian-norgie-shirt.html
FWIW: I chose "A-grade" on the web. I bought the first one from their stall/tent at a Land Rover show a few years ago.
As for sizes, the shirts are labeled in centimeters but the web has them tagged as s/m/l etc. For comparison, mine are labelled "108cm". If exact size is important you can phone them, they're ever so helpful/friendly etc.
WARNING: That site is addictive