The AC3200 has the same processor as the AC68U, I would assume the drivers would work given you're on the same version of Merlin with the same kernel.
The tomato extras would theoretically work given that the kernel used is also the same.
Sorry for such a late post, might as well keep this long time thread running.
I just noticed the same thing as soon as upgrading to 380.63, so I went ahead and did so for the RT-AC68P. Download here.
It's unfortunate that there's no real definitive guide for doing so.
Here's what worked for...
Also running into this problem, still as of this post. I wonder if there isn't something broken about the build method or if it's changed permanently.
All I'm looking for in building it is all of the extra modules for the AC68U kernel, 2.6.36.4brcmarm
So while unlikely, if anyone has them...