One of the benefits of playing highland bagpipes is no one minds when I practice whistle
But seriously, in college you ought to have ample opportunities. Thinking back to my college days I could have practiced:
In the stairwell of my dorm.
In the lobby of my dorm (near the piano...)
In the common area outside my dorm.
In a parking lot on campus.
In a green space on campus.
Near the athletic fields.
In a practice room in the music building.
In an empty class room.
I could have practiced in my dorm room too, I suppose. People probably wouldn't have minded that as much as the loud stereos or electric guitars (think "11").
Whistle mutes are easy to make. I do mine different from the photo though. I take a narrow strip of card stock and fold it into a V. I hook the V onto the blade of the fipple, with one end going inside the body of the whistle. So the point of the V points towards your face and half of it is inside the whistle. This mute will quiet all the notes to whatever degree you desire (wider paper = less whistle), without impacting tuning. I rarely do that (see opening comment) but I did at a camp two years ago to play after curfew along with my friend, who plays harp, and it was perfect. The whistle responded normally, but it was barely audible.