I have an extremely wide, exceedingly flat set of feet. Shoes are a serious challenge for; I have to have my dress shoes specially made by Alden. I normally wear an 8.5 or 9 in 4E width, but your feet swell when you walk, so that proves to be too tight for a day on my feet. There are too places to get the widest sizes.
1) New Balance, which makes a couple models in a 6E.
2) Wideshoes.com. They carry Hitchcock, which makes wider sizes, some New Balance, and a few brand that makes wider sizes especially for the website.
I took my hiking boots from New Balance and found myself footsore but not in pain at the end of the day. Wideshoes.com has a better selection in that size range, but I don't care for most of them.
Remember that because your feet swell (even if you don't have wide feet), you should buy shoes one full size larger than normal if you plan to do a lot of walking. My boots were size 10, width 6E, and they were comfortable without an extra bit of space.