victornet has them a little cheaper: 9/16-20 High Speed Steel LEFT HAND Plug Tap
The R hand threaded variant also there.

Seems like there is some confusion as to taper on taps, with some posters apparently
feeling the cranks should be tapped like gas and water pipes with a definite taper.
Since pedal threads are not tapered this makes no sense as only the innermost threads
would hold the pedal and it would wobble around in the outer most threads.

OTOH taps are sold in a variety of forms: bottoming, plug and starting. All have a bit of
taper in the initial 2 to 8-9 threads to facilitate starting the tap in the hole for start or plug
taps and with bottom taps the assumption is that the threads are already started, are in
a blind hole and the tap cuts to within 2 threads of the bottom of the hole. Some taps are
sold as re-threading or repair taps, usually these are carbon steel and not HSS and are
meant to repair bunged up threads and are typically plug configuration.

https://en.wikipedia.org/wiki/Tap_and_die

Mcmaster listing of tap types: https://www.mcmaster.com/#standard-taps/=16k1c7g