What sizes are you after? I stopped by a jewelry supply in town and they had fine silver sheets that were 6"x36". Perfect for the 2 1/4" square plates I’m going to play with. It’s also good enough for up to 5×7 but irritatingly short of a full plate. I wonder if you’d be able to solder two or more plates together with fine silver solder in order to get potentially any size. I’m sure the process would play hell with the joint though.
I don’t think anything is easy with daguerreotypes and I’m sure I’ve only seen the tip of the proverbial iceberg…