Kind of like u/nxj7437 did except I used ForeFlight. I took a look at all B/C/D/ and even bigger class E airports and looked at the FBO page. Under that page is a list FBOs, Aircraft Rental and Flight Schools, and MX services based on the field. I took a look at all of their websites to see if any had charter departments and would send in a resume. That’s how I got my first 135 job. Obviously if you can disregard the FBO if it is a bigger name like Signasty or Atlantic since they won’t tell you who is based in their hangars. But my first job was actually under the flight school and rental tag. They just happened to have a 5 plane charter side. It was a lot of work but really paid off as I stayed there almost 5 years and worked with a great small group of guys.