I have not seen any around. I am contemplating building my own. To me the 18650 is such a perfect battery size to run a decent output lantern. I am thinking a CREE might be too bright. Probably all you would need is 2 or 3 50 lumen emitters of some sort, with 2 or 3 18650s. That should give a fair bit of light that would last a long time. I will have to look into it a bit more.
I could get a cheap $15 lantern from ebay, rip out the fluoro tubes and cheap lead acid battery, then fit the new stuff. Should be heaps of room. Out in two 50/100 lumen CREES back to back where the old tubes were....