Why can’t I find the Quick Order Page app block in the theme editor?

The Wholesale Order Form app block is available only on the Product page template. It cannot be placed on the home page, collection pages, etc.
The app block is not compatible with 3rd party page builders like Shogun. If you used such a 3rd party page builder, and the theme editor does not recognize the template as a Product page template, then the app block will not be available for that page.