Qualcuno sa dove posso acquistarlo o qual è il “nome” o il tipo ufficiale di queste staffe da parete?

All diy stores have or at least had an assortment of this. Think hubo gamma brico. I think they are called versterkingshoeken or stoelhoeken. Depends where you ask but if you bring a piece and go to a diy they can show you where to find it.
Bolts and plugskes can also be found there.