Search Engines are what they are and are not necessarily created equal. So how you learn to use them is the key. That said any combination of terms that you are interested in should bring up some desired results if the engine is worth its salt. The search can be simple for a wide array of possibilities, or more detailed for just exactly what you are looking for. All IMO, YMMV.
I simply used "dual battery mech mod" as a first inquiry in Google since it was handy (and stopped there). But I could have also used other terms with them or in place of what I did use such as unregulated, box, mechanical, squonk, series, parallel, 18650, 20700, 21700, 26650, etc, etc, etc to narrow the search down to just those terms that I was looking for.
Good luck on your quest.