From my faulty memory back when the regulations changed: Yes, they can fly on planes if they are in the devices they are for; otherwise almost no small personal electronic in the last 5 years or more could be on a plane.
They can even be flown up to some qty if they are stored such that they cannot be turned on or short circuit and start a fire (Spares Carrier, anyone?). No they cannot be flown in bulk without being labelled hazmat and packaged appropriately.
Northern Security sells Surefire boxes of 12 for about $25 (I bought a box, put the 2 I needed in the flashlight that needed them, and promptly placed the box somewhere I wouldn't lose it after which I even more promptly lost the box). I'm sure that Great Northern Guns and Alaska Tactical have them as well. I expect the big box sporting goods stores do as well.
Buy American, or at least Japanese made lithiums. You don't want the cheap lithium batteries.
Read here. And here.