All I can say is keep looking. Millions of the things were shipped out, and you've still got a good chance of finding a new one right now. They are definitely disappearing from shelves, though.
When I decided I wanted to pick up Soul Silver, I actually saw a lot of places with copies of HG (already had). I found SS at three locations (four copies between them), and of those, two had damaged boxes, and one place put their price sticker directly on the box.
Used, these seem relatively easy to find. Damaged/missing Pokewalkers and boxes are common.
I'm always on the lookout for the games locally, and the ones that pop up the least are G/S/C and FR/LG. I still see one at least every couple months, though.