I don't make the straight penholders, which take the inserts - the inserts used to be available from Stiles and Bates, but I've just had a quick look and they don't seem to have them. I make oblique penholders, used for Copperplate and Spencerian calligraphy, which put the nib at a slanted angle. I make the metal nib holders for those myself. I used to turn the pens, but then I started making ergonomic ones, like these (there's no nib inserted in them, but hopefully you can make out where they go!) [ATTACH]32324[/ATTACH]
EDIT: Just found the inserts here