The Iseli hybrids are fairly common around here in IGCs, but we are a prime area for them in MSP because we really cannot do Japanese maples. People try and you might find the random decent specimen around here, but not reliable.

My guess is you are dealing with a combination of difficulties in propagation, slower growing, higher priced at retail, lack of awareness about them by the consumer and a rather narrow slice of the market in zone 4/5. I don't think even straight Korean maple by seeds is a huge seller up here. A. triflorum is rock solid hardy up here and very difficult to find.

The Jack Frost trees have become commonly available over the past few years. I had a hard time finding Ice Dragon, but even that one is starting to show up with regularity. Unfortunately, I don't think these hybrids are quite as cold hardy as promoted. I lost a nice-sized North Wind following the unusually cold winter of 2018-'19. I also lost an Ice Dragon this spring, which was purchased fully leafed out and planted about a week before the mid-May cold spell. In another post I had commented about a Ice Dragon that had been growing several years on the grounds of a nursery I visit periodically. I was there a couple of weeks ago and the tree was gone. I spoke to the owner who said it died following the 2018-'19 winter, along with several others they had sold. They will no longer be selling Ice Dragon.

I'm also baffled why A. triflorum isn't more commonly available in the upper Midwest. I know seed viability is low, but you'd think nurseries could overcome this obstacle. When I do see one available, it is usually in a wood crate and very expensive.

I'd also add A. mandschuricum (Manchurian Maple) to the list. Very hardy, vigorous, nice form, and great fall color. Whaas, you need to get yourself one of these! :)

I purchased Acer x ‘Cinnamon Flake’ last year from Davidsans. It was very reasonable for size and quality of the tree.