I’ve heard of some recipes where kitten or dog kibble are added to the mealworms along with other things. I read that rehabbers feed babies with a recipe that contains kitten kibble & mealworms. Our local rehabber does use both dog & kitten kibble in recipes to feed babies or sick birds.
The calcium powder is recommended for nestlings because mealworms are high in protein, but low in calcium. They need the calcium to make their growing bones/wings stronger. Some suggest to add calcium to ensure female lays healthy eggs. The reason why I’m trying it this season is because I had 2 fledgers last year that couldn’t yet take flight. At first, I was coating the mealworms more than I am now because my blues weren’t as receptive. Now, they have no problem with it. I bought a nice sized bottle of calcium carbonate powder for ~ $8 online. Calcium citrate is supposed to be fine too. Would think you could find it locally too.
Nicole 
(how birds reacted to calcium powder at first)