How do I send in my Apple Earphones for replacement?

I bought an iPod Touch 4g in Dec 2011 which came with Apple Earphones. They suddenly stopped working when using them one day and I'm pretty sure it is still covered by warranty. I want to send in the earphones for a replacement, but the nearest Apple Store is about 8 miles away and when I try to apply online, it asks for a serial number which is not on the earphones.

My questions are:

-How do I find the serial number of the earphones?

-Should I just call Apple Support to ask them about this?

-Is my only option to go to the Apple Store and give it to them?