if you want to buy american, ep buddy and battlepack.com both sell LiFe cells and packs.
http://battlepack.com/
http://www.buddyrc.com/battery/a123-life-batteries.html
K2 battery has a pack that has a board in in that makes LiFe cells act like a sla battery. they also sell single cells.
http://store.peakbattery.com/index.html