I agree it's a blind spot, but also a kind of arrogance and privilege. I know all about the unadvertised work world because I lived it for years. Many other Americans do too, but not the kind of people who frequent this forum. A gross generalization of course, but in my experience it is primarily naturalized white males, Hispanics of both genders (some immigrant some not), and African immigrants that are "fluent" in this part of our economy.
A lot of folks would rather throw up their hands and give up than do most the work I'm talking about - which is too bad because I've seen a lot of success stories start with "casual" jobs. And, in the age of "bullshit jobs" which everyone loves to talk about - a lot of blue collar low-skill work is actually not bullshit. It's necessary and important work that needs to be done, and a lot of it can hardly be automated.
I think you're overthinking it. It's mostly just asking around. Go to a blue collar bar and chat with some of the guys sitting there. In small towns the VFWs or Legions are good choices. Talk to the ones drinking by themselves and that look dirty or sweaty. Hang out at gas stations or a McDonalds. All the people that work these kinds of jobs need to use restrooms and eat. These are two very popular places for them to do those things.
Walk through an industrial park and ask the receptionist at each one if they're looking for help. I got several warehouse jobs this way.
Call lawn and landscaping services. A lot of these are small single owner operations. Most of these guys are too busy to look for people formally, but they can use the help. I have a buddy who runs a lawn service, he's paying $20/hr no questions asked for help. He's desperate to find people but he's not advertising on the internet because he's not tech savvy.
A lot of folks would rather throw up their hands and give up than do most the work I'm talking about - which is too bad because I've seen a lot of success stories start with "casual" jobs. And, in the age of "bullshit jobs" which everyone loves to talk about - a lot of blue collar low-skill work is actually not bullshit. It's necessary and important work that needs to be done, and a lot of it can hardly be automated.