You might try www.aircraftspruce.com They have economy push to talk switches that might do the job for you. Before you buy one though, call them and ask them how many amperes they're rated for. They maybe too light duty but, they're around $20 so, it maybe worth looking into a bit further. :smile15:
Here's the direct link. http://www.aircraftspruce.com/catalog/avpages/ptt_switch.php