Anyone ever hear of branch "refusing" assignment requests?

If your S1 pulled EDAS and that’s what’s available, that’s what’s available. And even what’s on EDAS, you may not get. You also have to take into account your MOS, years of service, strength of your MOS, the current priority of the duty station you want versus the priority level of what the Army needs.

My advice is that, as an E-5, take Recruiting, Drill, or Instructor. You will need to get your first broadening assignment out of the way at some point. This may be a good time for that. I also suggest you and your spouse fill out your ASK. That will give your Branch Manager more to work with. Utilize your Requisitions.

Branch works with you when it fits into their timeline. If you are OCONUS they have to place you on assignment no later than 6 months prior to DEROS, which is why you were assigned by 6 months out. Also, you received that assignment in Korea because that's where your HA/AP was set for. You may not have known it at the time.
Your Career Counselor and S1 are telling you the open requisitions. Being MACP, you aren't eligible to take any of those. What will happen is that your branch manager will have to dig into the strengths of various duty stations and when those assignments are available. The answer may be that you both go on a dependent restricted tour for a year with a follow on assignment putting you together.
The best way to approach your branch is for you both to send an email naming where you would like to go. Give 3-5 locations in order of preference and update your ASK. Believe it or not, they do look at that. If they don't get back to you, email the PDNCO. Sometimes the person you are emailing is on TDY.

Getting an assignment will happen one day, keep in touch with branch. But you also need to make sure you both are enrolled in the married Army couples program, and everything is up to date. That way your records will help you two stay together. Good luck