Souvenir shop - shopping around the Mouth of Truth monument area
There aren't any stores or shops near or close to the Mouth of Truth monument. The Mouth of Truth is located on a very busy street which doesn't even have a sidewalk on the side of the Church where the Mouth of Truth is located. If you'd be looking for a shop, the nearest one would be in the Trastevere area and to reach Trastevere, you have to cross the Tiber River on the nearest bridge.
What you can find though is a full stocked shop of souvenirs right next to the exit of the Church Santa Maria in Cosmedin. The store sells books written in a couple of languages with information about the Church Santa Maria in Cosmedin for 5.00 Euro, magnets, cups, pens and other articles you usually find as souvenirs figuring the Mouth of Truth. My favourite souvenir is the plate that looks like the Mouth of Truth. It's a small copy of the big heavy stone hanging outside.
When entering the shop the first thing you notice is an ancient mosaic picture hanging on the side wall. The storekeeper will gladly let you take a picture but you're not allowed to use the flash because it would damage the picture in the long run.
Inside this souvenir store you will also find more articles as souvenirs even if they have nothing to do with the Mouth of Truth. They sell postcards, wooden statues of Pinocchio for kids and calendars just to mention a few articles.
The store is special because it's actually part of the church and so the interior design is ancient. On the wall underneath the entrance door you can see two statues which are part of the churchs' interior decoration as well. Even if you decide not to buy anything, it's worth a stroll through the room and to have a glance at all the interesting articles this shop has to offer!