FWIW Jim at CBE can tinker with his existing designs too. I had him extend the base of his 45/70 Gould design and add a GC shank. All up the mods added approx 60 grs in solid form to his regular design. I also had him make a HP pin with several size pins, so I could produce solids or various HP bullets. It cost a bit to have made up but it is a very versatile mould.

You could design one yourself on the Mountain Molds site - at least that way you could design exactly what you want. I understand Accurate Molds will also adjust their designs to accommodate changes to the extent possible. So a few options for you.

As mentioned Buckshot on castboolits makes sizers and suppliers like Buffalo Arms are likely to have the sizers that you need.