Please help me find a specific shirt for work?

I am a teacher and I am looking for specific button down shirts that have a different stretchy material on the sides. I have one shirt that has this, and I have seen other people with this type of shirt, too… but I can’t seem to find them anywhere.

My body is proportioned weird, and these button downs with the stretchy sides fit wonderfully. Can anyone please let me know where to find some online?

Thanks!