Short answer, I know of no commercial nursery breeding specifically for bonsai traits.
Somewhere on the west cost someone is producing cork bark Japanese black pines from seed. They so far have been ''true to type'' developing real cork bark, though the vendors only guarantee 50%. My sample is small, only 3 were old enough to show bark, so for my oldest 3, I had 100%, sample size to small to predict anything about the ''average'' for the seed source. but I have picked up a few more this year, we will see what they do, a 5 to 10 year wait.
JM, satsuki and flowering quince breeding is being done in the USA, but mainly for the nursery/landscape trade. Fortunately, part of the landscape market includes rock gardens, fairy gardens, trough gardens, railroad gardens and other types of miniature gardens, so commercial breeding does include selection and development of trees with traits desirable for bonsai. The ''miniature conifer'' collections are a craze all unto themselves. Yes, especially with conifers, selection of the anomaly is done more often than actual breeding, but just take a look at all multitude of Chamaecyparis obtusa cultivars in the US and it is obvious places like Islei and Stanley & Sons have raised hundreds thousands of seedlings to find some of their choice little miniatures. Unfortunately to my tastes too much attention has been put into developing yellow and white variegated foliage forms of conifers, but that is my taste.
So there is no ''for bonsai only'' breeding going on, but lots of breeding for compact, dwarf, multiple bud producing cultivars (yatsubusa) and other oddities for the miniature, and dwarf plant markets. I suspect the bonsai only'' market is just too small $$$ to support commercial breeding just for that market.
How can I ''un-see'' a pink thong or Smoke's bevy of groupies?