I don't own every single book, but a quick look at D20PFSRD seems to only show the inkpen. The closest I can think of is Artisan's Tools, which I suppose would work for pottery or sculpture, or the vague "Masterwork Tool" which I suppose might be recorded as "masterwork paintbrush". If there are entries for this sort of thing somewhere, I'd love to know the reference.
From the Core Rulebook:
All crafts require artisan's tools to give the best chance of success... masterwork artisan's tools provide a +2 circumstance bonus on the check.
For making calligraphy itself, you're right- it's pretty much artisan's tools or nothing. If you're not looking for items specifically for making a Craft (calligraphy) check, however, might I recommend the following selection?