AZSmokeFree.com and VaporKings.com also have RN4081 stuff and I think the AZ one has a manual RN4081 battery I would recommend over auto. Manual RN4081 should be totally sealed metal on the threaded end so safe from juice leaks when refilling cartomizers etc. The RN4081 can be a 3-piece with battery+atomizer+cartridge aka cart, or a 2-piece with battery+cartomizer
Aquavaporcig also sells some RN4081 stuff
And NoSMokeVA.com has a super PCC that is for either 510 or RN4081 (the battery just presses in for charging so it works with either) and I use it with 510 manuals (the 2 battery sections are notched to allow space for battery buttons). So they might also sell some other RN4081 stuff there. I only went there to get the roomy PCC.