Where to get tsuugaku teiki (not JR lines)?

I am a college student in Tokyo and I recently got my student ID with a sticker labeled with my commuting route.
I only take the Tokyu Meguro Line which changes to the Mita or Namboku line at Meguro station, each day. (Musashi-koyama station to Shirokane-Takanawa).
I have a Suica card but I read online that I can't make a commuter pass if I'm not using the JR line.
I was wondering if I should get a Pasmo card?? Is it possible to get student commuter pass with Suica if I'm only using Tokyu Meguro/Mita/Namboku line?
I am very confused on the whole process of where and how to get a commuter pass for students and what to do with my current Suica card.
If anybody could clarify that would be great!

Go to the nearest Tokyu rail Station. Fill up the Forms.write your get on
Get off station, pay the money.That's it.
In Blink eye,it seems very difficult. But in reality,its so easy.In the Form,
You need your university's seal.Then you get discount.
As I am a worker,so I don't need uni seal,so no discount for me.

Yes, your commuter pass must be on a Pasmo; you can buy it at the same time. If you won't need your Suica anymore afterwards, you can return it at a JR station.

To purchase your commuter pass, just ask station staff at any Tokyu station (maybe bigger stations are more likely to have English-speaking staff).

Sorry, commuter passes are not sold at all Tokyu stations, and in particular not at Musashi-Koyama. They are sold at Meguro, among others.