There are through dovetails and blind dovetails. Doubt you can find a jig or template for 30" width, but you might be able to handle blind dovetails with a large dovetail bit and a CNC that can clamp boards vertically. I've often cut dovetails for students using a CNC from Probotix.com. They have two versions that are 36" wide and have an open frame that can be adapted for vertical clamping inside the frame. Board horizontal for the female blind side, and vertical for the other board to cut the male pins.I am looking for a dovetail jig that will handle 30" width and more important, 1" thick material.
All the ones I've reviewed only go up to 3/4"