hi
not sure on working out the current dc current rating for an ac rated switch, but you could use any switch, and run the ign feed thru a suitable relay.
If this is a newer car then you may have problems.
This is a job that i have to do on a weekly basis (im an auto spark), and on modern cars can be a proper pain, due to the immobiliser fitted as standard in almost every car built in the last 10 years.
If this includes your car, then you either have lots of work to do to bypass the immobiliser, or you still need to put your keys in the barrell, thus negating the use of a switch in the first place.
(bypassing the immobiliser or key system will invalidate your insurance, unless you notify them before you start. if you notify them afterward, they may cancel your policy with immediate effect)