I booked a one way PDX-LAX on united.com on an S booking code for $104.40. After a few weeks of watching the website, I saw the price dropped to $74.39 for T booking code. I quickly gave a call and got a $30.01 travel credit.

I'm trying to book my return flight LAX-PDX. It's showing $182.40 V booking code. I see on the flight availability:
F6, ... Y9, T9, S9

So there are 9+ tickets for S and t.

1. How do I get the S or even better the T?
2. Do I wait until united post them? (like my PDX-LAX flight)
3. Do travel agents have them?
4. Is it possible for United to skip the whole S & T and only sell other booking code?

Thank you.