Here is where I got the main components in my system. All items purchased within the last two months:
Selector switches: eBay user "jamesbondtb"
Pushbutton switches: http://www.auberins.com
Contactors: eBay user "hvacus"
PIDs: eBay user "2easy8"
Timer: eBay user "skiesmall360"
Alarm: eBay user "coolcheapworld"
PT100 RTDs: eBay user "procon-products"
And then, as a special note I would like to add that these: http://www.wago.us/products/2635.htm
made for very easy splices in my control panel build, minimizing the amount of wire I would have otherwise run. I found them at Menard's, a local hardware store.