In reply to abcdef:
sportiva yellow things (nepal somethings?) are available in 48 which I think is 13 and have a roomy fit I find, as I have got a pair. Scarpa Cumbre are also available in 13, and these should be built to the same foot shape as vegas. Last time I checked, Vegas and Cumbre were both made up to 48.
I found most shops will make you buy them before trying them on, but snow and rock in covent garden, and peglers in arundel were the only ones down south which where the would order them and I could try them out without paying £200. These shops could both get the scarpas and the sportivas
I think that Meindl are probably the roomiest of all, I have a pair of walking boots by them. I have heard they make them up to 14, though not sure that this is true. I think that Peglers can get Meindl, and the other german boots Raichle(?) so might be worth a try. Not sure if any of these boots are particularly technical though.
I always look with envy at people trying on boots in a shop wandering if they should have a larger size or not. If you have big feet you spend months trying to find somewhere with the boots and then you get to the shop and try on the size 48 and wander whether they will be okay.