Last time I went (4 or 5 years ago) to Bethesda in the Ogwen Valley North Wales, there was a chap hand-making boots at very reasonable prices.
Small shop on the left as you come in from Ogwen.
Probably on the right if going the other way..........
I see you do some climbing (I did until the bones gave way!), so you might be in that area ocasionally.
Similar problem (big feet big legs). I ended up buying the biggest Mustos I could find and wearing plenty of socks on the basis I wouldn't be walking far in them. Musto now (this season) have a pair of HPX boots like trail boots which might be worth your while considering. Otherwise it's size 12 1/2 and plenty of socks for you!