There's a reason they don't offer that kind of extension.

Take a close look at your steerer tube. Steerers are usually reinforced for the bottom inch or two where the crown and lower head cup are. That's because what's below that is cantilevered out without any secondary support. (Imagine what would happen if a fork failed at that point).

If you add a spacer pushing the crown race higher on the steerer you could go beyond the reinforced zone. Also extending the axle further away from the crown increases the bending stress at the crown. More bending moment applied at a less reinforced point is a recipe for disaster. No wonder nobody makes the extender you envision.