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My first thought was "I bet Rosco or Lee have something like that, but maybe not in the right size" and after a few minutes of searching, I found something from Rosco that's like that, but not in the right size. https://www.adorama.com/ro1081102024.html So there's hope, maybe that or searching for "graduated center filter gel" or similar would get you closer! Another thought would be to make something like the soft focus disc for an some types of large format soft focus lens - some examples here: https://www.largeformatphotography.info/forum/showthread.php?49632-Recommendation-for-Soft-Focus-lenses-for-4x5/page2 It wouldn't be exactly the same as varying the opacity of the film like in a gradient, but you could make an aperture that has a hard edge in the center with the edges around it perforated, but with the density of perforation decreasing toward the edges. It'd almost certainly introduce some interesting aberrations.

Hm, it seems to me rather like Jean-René douze-fps but I could be wrong!

The bottom right dude, is that the notoriously dageurreotype-shy, Louis 'Rolling' Shutter?