like OKP mentioned you can build a simple "loop key" with the XT-90 anti spark:
https://endless-sphere.com/forums/viewtopic.php?f=35&t=72687&hilit=xt+90+loop+key
I did it a bit overboard, but that's a step-by-step to build your own.
There's also pre-made anti-spark switches at DIYes and Enertion:
DIYes: http://diyelectricskateboard.com/product/on-off-high-voltage-anti-spark-power-switch-2-14s/
Enertion: http://www.enertionboards.com/electric-skateboard-parts/high-amp-120A-electronic-ignition-on-off-switch/
You can use a resistor with any loop key like this pre-made option:
http://graysonhobby.com/no-spark-hi-current-sermos-arming-switch.html?utm_source=google_shopping
If you are comfortable with surface mount soldering, there's also Vedder's anti-spark switch. You can get 3 PCB's from OSH for about $20, and the components from Mouser are about $7-10 per.
I would not suggest the Vedder anti-spark switch if you don't have good SMD solder skills (reflow oven or hot air setup). I have a few left if you are comfortable w/ SMD.
HTH - GL!