home depot has lock sets keyed alike, theres a number on bubble pack you can match up with others in box.
I just did 2 doors deadbolt and all are keyed the same.
what the guy above said.
Also at HD, and many other places:
http://www.kwikset.com/SmartSecurity/Re-Key-Technology.aspx
do you own re-key and it is not very expensive. Lock Smiths charge an arm and leg, especially if they are coming out to your house to do the work, not saying they are not necessary, but for something this simple your options provided at Home Depot might be a cheaper and more simplistic path.
I would pull all the loks and take them to a locksmith. Thats pretty easy to do. I had mo home rekeyed. I need to do the same for my new home in WV.
Avoid any Smart Key type of locks like the plague, especially Kwikset. They are horrible and the majority have some sort of issue when you try to rekey them.