I might be misunderstanding the question, so if you’re looking to make an existing android device you have work like this, please ignore the below.

Maybe a Google Nest Mini would do what you’re looking for? It’s definitely got the ability to be interacted with entirely verbally, but I guess the downside is a smaller selection of apps that do work with it (there is a list on the Google store of which apps it works with)

I think posters/flyers are one of the most powerful ways to reach people in a local area, you’ve got to be in the local area to see them, right?

Another way to spread the word can be via the internet, Facebook is god awful, but a lot of communities will have something akin to a noticeboard that is another effective way to get the word out.