It seems that the merchant selling the lower level custom spells is bugged. They will be displayed to some characters but not others, I believe it might be a bug due to their being in the Patrician category, which offers a different dialogue and price.
Sugriam still won't offer the custom spell scrolls to my Patrician. None-Patrician characters can see them however.
I was not aware there was a different store for Patricians. Annoying.