> Are there really no people that can at least bootstrap things for me?
There are, it's whoever assembled your meetup/function/etc. Getting a bunch of people in a room together who share at least some kind of commonality is a borderline magic trick, and it's a ton of work.
Your job is to pair it down from there, because you don't have anyone who knows you well enough to do that last mile for you. You might get there - if you make good friends with organizers, you will be the person they introduce new folks to.
> How am I supposed to invite new people to the comic book shop..
There's two elements to this. One of which is just actually leaving your house to go to meetups or places on a regular basis - find your local board game shop (or other interest - hiking, old movies, food, etc) and go to that thing with some regularity.
The second element is to talk with folks. Maybe even folks with whom you don't have a connection yet, but enough to exchange your lists of interests and whatnot. If you struggle for things to talk about, use tools like FORD (Family, Occupation, Recreation, Dreams) or the interview strategy ("Oh, and what got you into hiking?").
You don't have to have a deep connection to have folks you enjoy spending time with, even if it's just playing Catan once a week - but that's at least your bootstrap.