How to preserve coated popcorn

I think this is primarily going to come down to the method of cooking and the flavorings. I think it's unlikely that you can buy a microwave popcorn that will taste like the movie theatre.

You'll need a specific popcorn pan so that you can stir the popcorn continuously and that will also vent some of the steam from cooking (which a normal pot won't do. Whirley Pop seems to be a common solution here.

Next you'll need to find the right type of oil. Experiment with a couple of things to see what you like. Coconut oil seems to be commonly recommended (and not easy to find).

Finally you'll need flavoring. Try Flavacol. My work has popcorn on thursdays, and they use this flavoring. It's pretty dead on.

I don't think the actual pop corn kernels will make a ton of difference. It's more the cooking technique and other ingredients.

Here's my primary source, but further research and experience backs that up as pretty dead on.

How you are popping your corn makes a difference.

Air popped corn with flavoring added afterwards may be healthier but it is difficult to make flavorings adhere.

Using an agitated oil popper and putting the flavoring infused in the oil will make the difference. The flavors will be part of the kernel and not just stuck to the outside.

Lately I've seen several table top, agitated oil poppers at places like costco for reasonable prices.