Ultra Large Wet Plates. 24X48 in

I'm assuming you mean inches in your question?
youd have to have a lens that will cover that size. Unless you intend to shoot pinhole images.

A normal lens for a plate that is 24"x48" would be roughly 54" focal length or 137cm or 1370mm lens. Not many of those out there. I think there is a 1000mm Germinar not sure if it would cover the plate fully though (maybe thats okay). The "normal" focal length basically coming from the diagonal of the plate size (53.7" +/-)
You might want to try and get in touch with John Coffer, he shoots mammoth sized plates (20x24) and might have suggestions on lenses for that huge a plate.
I hope you have ALOT of working space. I've shot a bunch in the 8x10 and smaller size range, and a handful in the 12x20 size and it is a whole world of difference (the painful kind). Can't imagine trying to pour collodion on a plate that big, how much silver nitrate you'd need, and much less varnishing a plate that large....
Would be fun though and I bet the plate would be a thing to behold.

Hopefully some of the more knowledgeable collodion folks (smieglitz, billschwab, kerik, etc) will see this and chime in. They likely will have more info.

 

The lenses are out there if you have patience. I have a 1250mm brass lens from 1890s Belgium that is almost like two stacked coffee cans. I've seen at least one similar lens on eBay this year.