Indoor window trim company?

This is a weird request but, we're looking for somebody who does window trim like this for a kitchen window.

I'm only finding people who do window treatment, or window installation, but not the trim. We asked a general contractor who told us to measure and go buy the pieces ourself and he'll install them, but we're looking more for somebody who specializes in this.

We have no clue what we’re doing, and we’re nervous about measuring incorrectly or buying the wrong materials. Ideally, we’d like to find someone who can handle the entire process—measuring, sourcing the materials, and installing the trim.

If anyone knows of a professional or company that specializes in this kind of work, we’d really appreciate your recommendations!