I have a 3 wire supply to my oven #8 black, #8 white and a bare copper wire. Both black and white are hot - 120V on both to the copper wire. I just bought a new 220V oven that is 4 wire - black, white, red and copper. How do I hook it up? Black to black, red (oven) to white, white (oven) and copper to copper?

You cannot use this circuit.

Your new oven requires four wires, two hots, a neutral and ground. This is a 120/240v circuit.
Your existing circuit is 240v only and has only to hots and a ground. There is NO way to wire the new to the old.
Sorry.

Please don't let anyone tell you about old 3-wire circuits being allowed, this does NOT apply.