There are many hatcheries that you can order from just about any time of the year.
It really depends on how many chickens you want as to which hatchery you choose (some have minimum orders).
You can also look around on the web to see if there are any local breeders in your area, you may want to post on your state thread here on BYC and ask if anyone knows a good breeder. Craigslist can sometime be another source.
Personally I used a hatchery (Meyer) to order chicks from since I was a "first timer" so I could have them vaccinated and the minimum order was 3 chicks since I was ordering in Summer (July). I have been pleased so far with what I have. I have 2 Buff Orpington girls, 2 Barred Rock girls, 2 Silver Laced Wyandotte girls and a Buff Orpington boy.
I brooded in the coop since it was most convenient, there are several threads on brooding outdoors so be sure to search at the top for articles and tips on that subject.
As far as choosing a breed, all of us have our own opinion as to which is best. You need to consider what you are getting chickens for in the first place. Do you want just egg layers, dual purpose (meat and eggs) or something more ornamental.
Other things to consider would be the weather you will have, do you need cold hardy or more heat tolerant.
Here's a few hatcheries to get you started, but there are plenty of them so the best is to do a web search to see what's out there:
https://www.meyerhatchery.com/
https://www.mcmurrayhatchery.com/chickens.html
http://www.mypetchicken.com/
