Good luck finding one that short, at least one of the historical brass Petzvals - most of them were made to be much longer than what we would consider normal for the format so that they could use only the sharp, unswirly central portion of the image circle. Most CDVs (very similar in size to a modern 6x9cm negative) were shot with 8"+ lenses. You might have some luck finding a loose lens from one of the old penny picture cameras that had six, nine or even sixteen lenses to make a whole bunch of identical, small images on a single sheet, but even that can be hard, as they're now collectible.