There area few types of these dwarf columnar Norway Maple clones around. Perhaps the best known is the cultivar Acer platanoides 'Rezek' (of Ed Rezek fame).
The late Bill Janssen of Collectors Nursery was always on the lookout for these mutants too. Scouring tens of thousands of seedlings for these dwarf oddities. He & Diana had a planting of them in their display garden and many years ago shared a few scions with us. We lost a couple along the way but still have one of the red leaved selections & one of the green growing in the garden. Great plants so long as you are not in too much of a hurry ;^)..
About 8 years ago we planted a stock hedge of different Stewartia including 10 Stewartia sinensis. one of them turned out to be a very compact & tight growing form. we're planning to move this into a better garden spot this winter & then see if it's worth doing anything with!
A friend who is moving next year & can not take his plants with him decided he didn't want to drag all his heavy pots of Brugmansia, Musella, Ginger & Cordyline into the Cold frame again for the Winter so he asked if I would be interested in them! Guys Plant Shelter Rescue Service to the rescue :^)..