A potter to collect whenever you see her work come up is Karen Schuman, out of the kiln at Oakton Community College, Oakton IL. Some of the finest high temperature fired pottery I have handled. The feel of her pottery, with smooth burnished unglazed pots is just fabulous. Very thin, even smooth walls on wheel thrown pots. Collect her now as she has retired. I don't think she fired any pots in 2018. Her output was never large, not all of it was bonsai pots. So if you see her work, feel it, you will buy if you actually handle her pots. She mostly made pots for medium to smaller trees. Some of us local Chicago bonsai folk are trying to talk her into continuing to make pots, I don't know if she will or not. Snap them up when you see them.
The list on American Bonsai Ceramics is pretty complete.
I like John Menzel, he is relatively new, only recently began selling bonsai pots. He has been a decorative goods potter for 10+ years, bonsai pots for maybe 4 or 5 years. You might find his pots at Hidden Gardens. Eventually he will have an internet site.
Ching-wen Cheng, out of California, Sam Miller, Dan Laxdal, Brian Soldano, all are potters I love, and for slab built rectangles you need to look at our BNut stalward, Sorce. Also BNutter Stickroot and ???? I'm blanking a name here, damn, I'm getting ''sometimers'', as in sometimes I can't remember shit. Anyway, I really enjoy collecting pots from American potters. Usually I buy a pot on impulse. Later I will try to find or grow a tree to fit the pot. Rarely do I look for a pot for a specific tree. I do look for pots in the sizes I most commonly use. So I tend to buy pots for medium to larger size of shohin and Kifu, and only a few large enough for larger sizes.