Tal to Lyman, Rapine, and NEI companies. You should be able to find websites for them. I don't know that any currently make such large diameter RB molds, but they all can. Its only a question of money. And Dixie makes their Scissor mold for all kinds of RBs, too. It doesn't have a cut-off plate, but you can hold the ball, cold in the mold with the sprue up, and use a medium or fine file to file down the sprue flat with the mod. That give you a consistent RB. The Tanner molds are made of brass, and I would be reluctant to use a file near this softer metal.
Rapine made a custom bullet mold for me, and later added it to their line of ready made molds. I paid a bit more for my mold than they are now charging, but I got what I had wanted for more than 25 years, and could not find.