Considering that you had to play the game 3 years ago, within a 4-day period and on a Mac to get them, I'd say they're probably rare.
I didn't know they were rare until I looked them up, and he probably didn't either. I used to play a lot of TF2 back then and I seemed to remember seeing them a lot so I didn't think it was rare.
Also, it wasn't 4 days. It was extended into the middle of August (as per the TF2 official wiki). I got my Mac on the 25th of June of that year and I have those headphones so the wiki is wrong.