If you can live with a 15A switch, look at a Honeywell 2TL1-10. It is a mil-spec toggle, double pole/double throw.
Bear with me on this description...
One side is configured (starting with the toggle down), OFF - ON - ON. Other side is OFF - OFF - ON. You get toggle down, both circuits off. Toggle centered, one circuit on, one circuit off. Toggle up, both circuits on.
Be sure to check both sides with meter to determine which side is which. Terminals are numbered - 1&2 are one circuit, 4&5 are the other.
Only down side -cost is north of $30...
Ray