This looks like the right one for your GPS. Can't say much about it as my GPS is much older so uses a different style mount. But you can't beat the price of this one.
http://www.amazon.com/Garmin-010-11023-00-Colorado-Oregon-Series/dp/B0012MI7QE
*Edit: There's some conflicting answers on the Amazon page about whether or not this is for the eTrex 10. Garmin website recommends this product number as well: