when you finally make it easier on yourself on bottle cleaning/delabeling day by pitching the ones where the labels won't budge while soaking. Great Lakes & Small Town Brewing, I'm referring to you.
That is how I got most of my bottles. Rather than buy brand new bottles, I just shopped for filled ones with water soluble adhesive and pop-top lids. Saved a bit of money on shipping, and they came pre-filled!
I still find replacements this way...some people I share with seem to forget to return the empties back to me.