The question of where/how to find a partner can be tough to answer; so much of the process of finding partners (whether someone is looking for one-time casual sex, ongoing casual sexual relationships, or long-term romantic relationships) is going to come down to the luck of running into someone with whom you have a mutual attraction and similar desires when it comes to sex and relationships.
Right now, since it's not safe to socialize in person with new people, finding partners is a little extra tricky, but hopefully that will change soon. If you're interested in using dating apps or websites at all, a convenient aspect of those is that you can put what you're looking for right in your profile, to increase the chance that people responding will already be aware of what you want.
In terms of talking to friends about this, I don't think asking "would you be interested in exploring casual sex?" is necessarily going to negatively impact a friendship if they aren't interested, but it is a conversation to handle with care; if there are specific people you think you'd like to ask about this, we could certainly talk about how you might go about it.