If I'm reading correctly, you want to stop all sound coming from one side of the headphones. Is that correct?
If so, you could probably achieve this by cutting the wire to the speaker.
Do you already own a pair you could try this out on?
Do you know the model of the headphones you want to buy so I can find a picture?
...and you aren't wasting your time looking for single ear headphones, I've seen them before somewhere.
http://www.topdjgear.com/stanton-djpro-300.html
Also, consider a
Headphone Amplifier