Where can we get them?

People are awarding them to users on https://badges.page and https://nostrbadges.com Anyone can create them and award them. It's up to the user to accept it.

How to rely on the “badges.page” site? While we should enter our private key? It tastes like a “Manipulator-in-The-Middle”. I will recommend NIP-07! https://github.com/nostr-protocol/nips/blob/master/07.md