I wanted one these sights from RJ for my No. 1 in 450/400 NE back in 2016 and he told me then the guy that was making them for him was no longer doing any production work. And further, RJ himself was not in the "sight making business". I ended up with a Skinner aperture sight (without an insert) that mounted on the rib and with the addition of a slightly bigger white bead in the front was totally satisfied. Plus I didn't have to worry about my hand on the pistol grip getting chewed up by recoil.
All that said, if someone finds one or if production has begun again, please let me know!