Character Expression/Pose Series Using Photo Characters?

The more specific one's request is for certain character traits and expressions, the more likely it is that filling the request will require licensing characters from a company that focuses on that service, buying images from a stock photo agency, or paying for a custom photo shoot. Or, as PeterRoberts536​ suggested, taking the photos yourself (though that still might incur expenses, such as hiring models, renting lights, etc.). 

While Articulate does provide some cut-out characters, that's not the focus of their business. In other words, it's a limited selection.

Here are two sites that license cut-out characters:

• https://elearningart.com/
• https://www.elblearning.com/create-learning/asset-library/cutout-people

Note: Cut-out characters from other sources are put into Storyline via Insert > Picture (not Insert > Character). For Rise, you could use photo software or even PowerPoint to combine a character and a background into one image. 

Use any background you want behind cut-out characters. For one of my clients, I took photos of their building when I was there for a meeting, and used those behind cut-out characters.