I'm a size 11/11.5 so I feel your pain. I was actually in Macy's Herald Sq store in NYC this weekend (one of the few Macy's that actually have a good selection of large size shoes!!!) and I noticed alot of 10.5's from Nine West. I walked away with Coach sandals in size 11 marked down from 140 to under 50bucks!
I also have good luck at DSW.com (the store by me is awful), Nordstrom/nordstrom.com (their brass plum jrs line is pretty affordable), and zappos.com. Shoemall.com and shoebuy.com have been lucky for me this summer and they usually have a web coupon. I've also snagged some higher end shoes from Bluefly.com
To the poster above 11.5 actually does exist!!! But only if you go to the likes of Stuart Weitzman, Taryn Rose, Christian Louboutin, and Manolos....lol. Then again, this is the budget board and I've had to buy my Weitzman's at Bluefly.com on clearance!