Most of mine were still on the top box of my GS when I sold it, I meant to take them off and forgot, the bloke who bought it seemed happy enough for it to go on its way with the stickers still attached.
We only managed to get stickers for about 1 in 5 passes on our trips, but did not always stop at the top, but made a point on some of the most famous passes only to find they had none.
At the Stelvio you can get stickers, T-Shirts, Jumpers, Watches, Wall Clocks and Stelvio 1/1000 scale Patio's (I probably made the last one up, but I did not go into every shop)