I was over on the Alpine area when I managed to get Sheik, they had some Toon Links too. I was over in Cascade when I got Rosalina, they had a handful of Sheik and Toon Link but they sold out quickly.
If I consider any retailers to be a secret spot I would definitely consider the Cascade Target to be a sweet spot. I stood outside the Alpine Target for twenty minutes during the storm we got on the 1st, managed to not get any amiibo, drove to Cascade that took me longer than expected because some people were driving 30 on the highway (which was semi-understandable given the weather conditions at the time). Managed to get there around 8:40 and they still had 3 Rosie and some Sheik and Toon Link. I've been unable to locate a lot of semi rares though, and I've been searching all over GR. Toys R US on Alpine is where I managed to get my Villager though.