I love this thread, especially since I’m casually looking for my next young horse right now…
My mare came from: http://www.emeraldacrestk.com/
Anissa has recently had foals sold in vitro for the most part, and many of the babies go on to eventing careers, but she was amazing talking to me about what I was looking for/wanted, and everything she told me about my mare before I got her about her personality, tendencies, strengths, was dead on accurate. She also knew my mare was meant to be a dressage horse - anyone on facebook who saw my recent “gallop” in the desert video knows she was right. 
Iron Spring Farm and Hilltop are of course big names with dressage breeding.
There are also lots of other smaller breeders who only have a foal or two a year. My trainer and his wife have been breeding KWPN but don’t have any for sale yet, since my trainer can put training on them himself. Plus, they started for themselves so haven’t figured out who to keep as their own future rides. Their babies have regularly done VERY well at their keurings, beating out many of the spectacular DG Bar babies mentioned above. 