Thing Called Sarcellus has made a couple of things, but nothing to my knowledge is posted online.
The fan art evolved with the series, and a couple of folks, specifically Quinthane and Somnabulist (aka Spiral Horizon), did more and more art the longer they were around. Because of that, there's more artwork for the later events in the series.
There's nothing much for sale anywhere. For one, Bakker is decidedly against monetizing his series beyond the books themselves. This is a barrier to putting things out there as people would likely feel guilty in doing it without his permission (which he hasn't formally given or denied anyone afaik), and doubly guilty because there's no direct way to give some amount back to him.
So yeah, what you see is what you get. Most everything regarding art is posted on the PON wiki, here, facebook, and deviantart.
Some people have made stuff for personal use - tshirts, bumper stickers, etc. but again nothing for sale that I'm aware of.
If anyone's got other trinkets though, please share!
