Hard to find, are you on UKV as SJP on there makes them, that's where I got my wooden serial/parallel mech one from and it's the only one I have seen that takes 18350, and that takes 2 of them, but he doesn't make to order any more, he just makes a mod then puts it up for sale.
Most others are either LiPo or 18650 regulated mods like the iStick [China, LiPo], VaporShark [USA], IPV [China, 18650] or Hana [USA, 18650] (only the Hana has been cloned), the VaporShark has both versions a DNA and rDNA (rDNA being the 18650 one) and the 40 is due out soon, I'm already on the waiting list for the rDNA40 one at GreyHaze, got 15% off using an AAEC code.
Only other option is to get Ian or someone else to make you one.