The thing about badger is that a good pelt has very full, thick fur that gives a "halo" effect larger than the bag itself. So to get a proportionally smaller sporran you'd either want to shorten hair around the perimeter of the bag or make the bag about 1.5 inches smaller in height and width. You can make up somewhat for lost room by adding some depth to it. Or a combination of both.

I could provide the smaller bag unclipped, and you could take it to a pet store and have it "groomed". If they didn't chase you out or report you for animal cruelty.