Yeah I found the general size by tracing my foot on a piece of paper and then you do measurements, payless has a chart that tells you size based on inches.
As for chain stores with size > 10,
kmart.com has some nice shoes in size 11 and occasionally higher, so you might be able to find them in stores too. Honestly if you do the measurements, I found using
endless.com to be very handy -- they ship free (sometimes overnight!), and have free return shipping, so you can just try a bunch of sizes and then return them with no cost or hassle.
The other thing is that sizes won't match even in the same brands -- sometimes I'm a 10 and sometimes I'm size 11. And if you're wearing girly shoes (as opposed to girly sneakers) whether or not you wear socks with the shoes can make a big difference.