Japanese maples are grafted because 1) its a faster way to propogate a desireable strain, and 2) it gives the maple the advantage of a root stock that may be better suited to your area, or more disease and pest resistant.
I don't know why you would object to a grafted tree???
As long as you keep trimming the sports from the root stock, you have a healthy tree that is the type you asked for.
"Sports" are the sprouts from below the graft - they are the original root stock tree trying to grow around the graft. You just cut or pluck them.
If the grafted portion of the tree produces seed, it will be the same seeds that an ungrafted tree of that same variety.