What is the crank that was stripped? Side? Length? Model?

Some new crank arms can be quite cheap. Check your local bike co-op if you have one.

How badly is it stripped? Some people have suggested possible threading a pedal in from the back side to repair some threads. .

I haven't done the crank helicoil, but I've seen Tandem cranks that have been helicoiled, and look very good. I did something else a long time ago, maybe a spark plug, and it lasted for as long as I needed it.

I do have standard 9/16 pedal taps around here, but not helicoil taps which would have to be larger.

The thread pitch on the helicoil taps should be dictated by the threads on the pedals at 20 tpi... but I guess not.

Var Taps: 5/8 x 24 tpi
https://www.vartools.com/en/9-16-x20...t-var-p396.php

Unior Taps: 5/8 x 24 tpi
Unior Pedal Tap - 5/8" x 24, Right
Unior Pedal Tap 5/8" X 24 Left
Unior Pedal Tap and Thread Insert Set 9/16"

So, VAR and UNIOR should be cross compatible. I'm not seeing EDI.

It looks like Niagara sells individuals.

Tap handles are common, and any machinist or machine shop should have lots of them.

Oh... if you're doing the right side, you might get away with a 5/8 x 24 tap (without the reamer).
https://www.amazon.com/HSS-Right-Han.../dp/B008B1NIRW

It looks like 5/8 - 24 Left taps are also available if you hunt for them.
http://www.ebay.com/itm/5-8-24-GH3-H...-/222050565365

A taper tap might be a little better, but the plug tap should work.

Without the built in reamer, the machine taps will need the holes pre-drilled.