After searching extensively, I don't believe that Amerock has a knob with the description that you give. What you can do, however, is purchase a wood Amerock knob and paint the middle of it black yourself. When you do this, make sure to put tap around the outer area of the knob, where you don't want the black to be. Then, paint the area of the knob that you do want to be black and remove the tap once the paint has dried. You'll have your beautiful wood Amerock knob with the black interior!
You can find it in edgeville. Its a wooden portal with a green center.
as soon as you find a Pokemon center.
A close one is right at the center of the milkyway. But you can find them anywere a large star exploded or the center of galexys.
in nimbasa city in a house near the pokemon center.
Black holes are in outer space, far outside our solar system. Most galaxies have a large black hole at the center.
Maybe in the daycare center?
you could make your own design for your backround
woodencrate.com
After you beat Team Aqua at the Weather Center, and cross the wooden bridge, May will initiate a battle with you. If you beat her, she'll give you HM02 (Fly) as a reward.
The poke mart is inside the poke center now. Right when you walk in.
Custom wooden signs are in high demand these days, and you can find them at Al's Toy Barn. The trees want your money! I want a custom wooden sign too.
You find it in a house in Nimbassa city. Just go from house to house around the pokemon center and you should find it.