I get mine from the local feed store. I am not certified organic so that might make a difference to you. Do you have any specific criteria that would cause you to mail order it? I think a vast majority of us get feed from the local feed store and most of the rest mix their own.
The type of feed you buy really depends on the chicken's age. If they are little chicks, I use chick starter/grower. The brand I buy is what TSC sells, called Dumore. You can feed your chicks this food until they are 20 week old.
Now, if they are hens that are ready to begin laying, then you want 16% layer food, which gives their little bodies the nutrition they need to lay those wonderful eggs.
I buy Dumore, but you can get any brand, really. For laying hens, I like the pellet form instead of the crumbles because there is less waste.
I agree with the other posts. It seems that most feed stores have a chick starter/grower and then a layer feed. The difference being the % protein of the feed. It seems like the chicks need somewhere between 18-20% protein and then when they start laying it goes down to about 16% protein. Definitely check out that link to the OSU extension service and keep checking back here for different advice. Good luck.
Get yourself a nice book, like Chickens for Dummies. Plenty of great answers and good to have as a reference for the middle of the night when something has chomped on your chicken, or your chicken looks funny, and figuring out what to expect. I checked them out from the local library first and Storey's Guide to Raising Chickens, and both are really good books.
You'll need to give them some grit, and some calcium in the form of oyster shell for promoting good shell production. When you eat eggs, save the shells, crunch them up and feed back to them too. If you have cracked eggs, you can cook them up and feed them back to the chickens for good protein too.
You might cut a piece of scrap vinyl flooring to put down to help protect the floor, then pine shavings on the floor 3-4" or so, and toss some chicken scratch daily to get them to scratch in it and stir the bedding, to keep it from matting down, and forming a stinky matted mess. That will work in the nests too.