The Korean Maple you're talking about is Acer psuedosieboldianum? If so, I've seen this variety and it is quite striking in autumn, has smallish leaves, and is quite cold hardy.
http://www.mountainmaples.com do a search on A. psuedosieboldianum...
I see no reason why it couldn't be worked as bonsai...Leaves are a bit on the large side, but I know they can be reduced, as I've seen some in ground specimens at the Nat. Arboretum with small leaves.
I have seen a few other references to Korean Maple as Acer barbinerve which is actually red twigged Korean maple and a completely different tree. I've also seen reference to this tree as Acer shirasawanum. Make sure it's not either of these.
Forget A. Griseum. It's frustrating, sadistic bonsai material.
it will not reduce
If you want to actualy do bonsai in the next five years or so, forget using seeds and cuttings...
