You can have a hollow point made by
http://www.hollowpointmold.com.
I'm considering doing it with my 170 and one of my 195 grn cavities.
I think part of the problem is demand. I don't think there's enough demand as most people prefer modern firearms. And those who do like these old guns seem to, overall, go with RB's.
It was the availability/cost of FN bullets that caused me to have a custom mold made. But I also liked that I could have it designed just how I thought it best, and not what someone else had in mind. I don't see any other cap n ball bullets heavier than 255 grns and with a FN.
But I also had mine designed so that they were as short as possible since powder capacity is effected. And then I also had the driving bands made wider than usual to create more pressure, which increases velocity. And then the width of the nose is wider than most so that it creates a larger wound track, but it also helps keep it shorter.