As the topic title, I tried to find them but cannot get any informations about. They are a sort of SMD tact switch made only by a very thin curved metal sheet. When you press they flex and make contact with the pcb or similar. I would like to post an image but I cannot find anything.
If you're talking about the part that flexes, it's called a "dome" or "snap dome". Photo from this site.
Digikey carries little SMD tactile switches, barely more than a thin piece that kind of pops down when pressed to make contact. https://www.digikey.com/product-detail/en/e-switch/TL3315NF100Q/EG4620CT-ND/1870400
Dome is apparently purchasable too:
Keypad domes are designed to be placed on PCB, not soldered
So something needs to go over them to hold them in place.