In the Steadicam JR instructional video the recommend a pistol grip to use in the shoulder mount mode. So, where does one find a pistol grip with a 20-1/4" screw at the top?

The one in the instructional video looks like it's an old Sony camcorder accessory.

You can buy a 3/8" pistol grip and use a 3/8" to 1/4" converter.

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=283348&is=REG

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=163361&is=REG

Kind of expensive though, might not be worth it...

I happen to have one of those "Sony Pistol Grip"
(with 1/4-20 mounting thread stud, lanc zoom, pause & standby.)
this one has a custom cable modification...the original length is way to short!
Will sell or trade for airline wireless mics,
Canon or Bogen Lanc zoom controlers,
Sony "L series batteries" or
any interesting training DVD/Tapes for camera supports...
(no need for software training titles)