Do a Google Search for the city-town you are interested in and add "Restaurant" to the search. Not all of them will have web sites, but Yelp would have them listed, and they'll be listed or identified on Google Maps. You will find you will need to get away from the main tourist areas to find them. Another thing, they are very seldom, if ever, open 24x7. Usually just a short window of time before lunch to around 6 or 7 pm. And expect a wait period to get a seat. The locals know these places and support them.
There are still many Mom-and-Pop restaurants in Indiana, but they are all small country towns or at some obscure location in somewhat larger towns or cities (at least in Indiana they are). Google works well locating them, but you won't find them anywhere near the main drags or interstates any more it seems. The big chains have monopolized those locations.
We don't drive interstates anyway, unless it's completely unavoidable for where are destination point is. Maybe that's how we find these places. It seems they are never on the main drags.