Just some ideas, not solutions:
Would lights with a 6v LED be better suited to 2xLiFePos?
The Convoy L2 can run 1 or 2x18650s so should be able to handle 2xLiFePos (most likely at the expense of LVP), are there other lights with this driver in them?
Lights that can run a CR123 that have a readily available extension tube might work, such as the current Armytek lights which are designed for interchangeable battery tubes so their 18650 lights will run from a single CR123 and also from 2x18650s with the right battery tube. (There’s also a promo on until Feb 10th as advertised in this thread: ARMYTEK OFFERS and PROMOTIONS)
And you could always look at 2, 3 or 4xAA lights if you’re going up in size anyway 