I get alot of questions/comments about where I buy my shoes because I wear a size 11. Being a size 11'er I know how difficult it can be to find shoes but although it may seem impossible it is really not. I find that many stores dont carry size 11 in house but most that have online stores do. Here is a list of some stores that carry size 11.
Rainbow, JcPenny.com, Charlotte Russe, Target, Justfab.com, Shoedazzle.com, Payless
Macys.com, Nordstrom.com, Topshop.com, Asos.com, Aldoshoes.com, NastyGal.com, Barefoottess.com, Zappos.com, 6pm.com
The only other tip I can give is to buy it when you find it because one thing I have learned is that size 11+ always sell out first. If it something you can live without you can wait for the sale but most of the time it will sell out.