I made one stop yesterday and walked away with all of these. Not pictured are a second HeartGold case and a SoulSilver case that I got on a previous trip there.

I've also been pretty successful in getting free DS cases just by asking for them at GameStop, but I'll admit I haven't tried in at least a year. I figured they were gone by now.

Yep, been doing the same thing for years! In fact, earlier this year picked up a large lot of about 75 DS/3DS cases at my local Gamestop, which included titles like Fire Emblem, Fighting Fantasy, Izuna, and Commando: Steel Disaster.

Unfortunately living in a big city like Toronto I just get scoffed at with requests like these, probably cuz I'm like one of a hundred or so folks popping in to ask for free "garbage".

Why would they throw away the boxes?

The GameStops I've been to usually have a box full of tiny yellow envelopes, each with a DS game inside, the ones that didn't sell. They have them like that to free up space. So I'm guessing every once in a while they gather up DS games that have been gathering dust, pitch the case, and demote them to a yellow envelope.

Yeah space is at a huge premium in most gamestops. So they throw out some stuff you might be surprised at.

I'm about to go dumpster diving. See ya later.

becareful, I did that once at a gamestop and the china buffet next to it threw some lo mein on my head.
 

Sometimes they'll still come in with trades.

The one manager I know keeps the ones for decent titles in the back (that's why SNESNESCUBE64 got a Pokemon Ranger case and manual with his non-matching game that I elf'd him).   

There is a TON thrown out.   Get friendly with a few employees.   Most would rather give you stuff than drag it out to the dumpster.