In that case, with most of them not laying, I would not be feeding them a "layer" feed. I would try something like chick starter, or flock raiser, or all flock, or something similar.
Chicken feed comes with lots of confusing names, so look at the nutrition panel. You want protein around 20% (anywhere from 18% to 22% would be fine), and calcium around 1% (you can ignore any decimal places in the calcium amount, but you do not want calcium at 3% or 4% or higher.)
That does surprise me. For that many chickens, I would expect them to go through a 50-pound bag every week or so.
For now, I would probably switch to a non-layer feed, stop the scratch and mealworms, continue leaving the oyster shell and water available.
It sounds like they have gotten in the habit of eating just scratch and mealworms and not much else, but that is not healthy for them. So they need to change their habits. Sometime in the future you will probably be able to restart the scratch and mealworms, but try not to have it be a big portion of their diet.
If you want to give a treat that does not cause problems: put some chicken feed in a dish, add water, and let them have it. Most chickens really love wet mash like that, even when it is just the same food they would usually eat dry. (Adding water does not change the nutrients, it just makes them feel like they are getting a treat, while they are still eating the properly-balanced food.)