How can I connect a zwave switch that requires a neutral to 3 way box?
If I understand your description, here is one way to alter your wiring:



Basically you use the existing white wires to extend the neutral node everywhere. Use the black wires to extend the unswitched hot all the way to the Zwave. Use the red wire in the third leg to bring the switched hot back to the first two lamps, which have their hot sides connected with the other black wire in the second leg.

For the last lamp on the right, disconnect it from its breaker supply and cap off the supply cable. Then re-use its former switch cable as a switched loop now powered from the Zwave. Check the total load on the breaker that supplies the box on the left, as you are adding one lamp to it.

As you see, you have more wires than you need. Cap all abandoned wires with small wire nuts. Don't just clip them short, I did that once and got a rocket from the inspector.

I have omitted the ground wires (the bare copper) but of course you will not.

Please allow me to express my extreme gratitude to you for providing me with the opportunity to draw yet another wiring diagram.