If the purpose here is similar to that in motor sports, that is an extremely visible device to disconnect the battery in the event of an accident so as to prevent fire, then go to any motor sports biased spare parts shop and get one where the 'key' can be removed from the switch; thus leaving it in the on or off position. This will have a major 'amp' terminal each side of the switch as it carries the full electrical and power load of your electrical system. It also needs to be carefully located so as to prevent 'grounding' on any body panel in the event of an accident.
If your requirement is for anti-theft purposes, then get an ignition isolation switch; much simpler device as it only carries a low 'amp' or power load and uses standard gauge wiring. This can then be mounted anywhere you choose, such as in the glove box or under the seat or any place your imagination may decide that a potential this will not think that it is hidden.
It will be simpler to install as it will interrupt the electrical circuit to your ignition switch, easily accessible under the dash board.