A few years ago I ordered 50 of these directly from Sorby and turned the rear portion down so they would fit into a 3/4" collet chuck and the teeth being only 1/2" wide worked perfectly for pen turning so if you can turn the rear section down this would be perfect.
I searched high and low and found nothing that compared. I bought one at Woodcraft that was supposed to be 5/8" but it turned out that the 5/8" was the diameter at the inner portion of the holding teeth but the outside diameter was 3/4".
Who know, perhaps someone who ordered one decided they don't need it anymore and might part with theirs, there were 50 members who bought one so maybe there will be at least one person!