they could if they had a casting plant in their back yard and had money to start.
it comes down to supply and demand. there was only room for so many aftermarket cylinders. from what i hear the banshee world isn't doing so well as far as cash flow. why would someone at this point in the game dump 100-500k in development when there is not a demand for it? calvin has the cast cylinders pretty much wrapped up. he produces cylinders that will outflow stock cases, exceed stress that they will handle etc. yes you can buy billet cases and keep climbing the ladder, but he also has cylinders that will still out flow those.
see where i'm going with this? no real point to duplicate what is already out there.
most builders can only get 10-15hp out of a cp cylinder after getting it from him and some even show up that can't be improved. the stars just happen to line up lol
not knocking billet cylinders, but bang for buck (tight-wad economy) calvin has what little market that is left wrapped up.