Help finding or constructing a new convertible top switch for my 68 Dart

Top switch from any vert operates the same but... the newer examples use relays to conduct the higher current so their manually operated switches don't need to be substantial in construction and don't need the large wires routed to them.
If you do go with a generic switch without relays, marine grade, whatever, make sure its rated at the amperage required for this application. Many modern marine examples are pizzy little manually operated switches for controlling relays also. When brothers boat motor was going up and down on its own, the switch was fine, a relay had failed.