What are some ways I should go about getting a tough assignment within my brigade before I PCS? Should I start emailing at the company level?

Interesting things on process. What's missing is the "why". What are you trying to accomplish and for what reason? You don't have to tell me, but a good CoC will want to filter on that to evaluate person-job-capability and likelihood of success parameters. BTW, tilting towards stuck in a rut, generically want something more meaningful, etc. tend to be nonstarters. I had my staff look at this stuff in filling a need and a positive thing for both the command and SMs long game. After all, you want something, but have to sell it. BTW, if you're not a good writer, stay away from the nasty Admin or JAGMAN investigations.

It is common for officers to write letters of introduction to brigade or battalion commanders. One page max. See the thread on RP on how to write one. Target it for your CSM.

Option 2. Get your ERB cleaned up, write down a synopsis of where your career stands (NCOES, last three jobs, what you think might be next, your goals), schedule an office call with your CSM before you get released from in processing, and gain his advice. It puts you on the radar for assignment/development lets the CSM put you somewhere he needs help and sets conditions for your career. Then follow through violently with your shot.

Contact your branch manager. Usually worked in the past.