How to implement a zoned low-voltage lighting?
I'd use relays for this
The simplest way to get out of this jam without throwing a bunch of lighting transformers at it would be to use single-pole/single-throw switches to switch on and off SPDT relays that control the lighting loads, as SPDT relay contacts can be wired in the same fashion as 3-way switches.  For the switches, you can use Leviton 56021s with Bell 5123 (single) and 5127 (double) weatherproof covers; you have a couple options for relays, though.  If you have space around where you're installing the switches, you can thread Functional Devices RIBU1C-N4 relays into hubs on the switch boxes; an alternative approach would be to use AP&amp;C PAM-4 relays mounted inside the boxes, but this requires a fair bit of box real estate at each switch location.  Both of these relays are rated for switching significant resistive load at 28VDC (7A for the PAM-4, 10A for the RIBU1C-N4), so 3A of LED lighting shouldn't be a significant challenge.