electrical stuff like wire and breakers/din rails can be found at places like digikey, newark, and mouser. Ebay and your local electrical supply should be able to help with some stuff too. The wire for the estop does not have to be very big. Current is what dictates wire size and if you are using PJ's estop that circuit wont pull more than 1 amp.
Check this chart out for future questions about wire sizing - http://www.powerstream.com/Wire_Size.htm
. I would go with the chassis wiring column.
Those distribution blocks would work fine. Just make sure you get them for the right wire size and current draw you expect. I got mine from mcmaster-carr and i think you can get stuff like that from places like newark.com if you wanted to combine the order with other things.