What kind of frosting has similar texture to the major grocery brands? I have a frosting conundrum. I like the texture of the major brands of frosting one might buy in a grocery store, like Duncan Hines or Betty Crocker or similar.

Specifically, I like that the frosting is dense and becomes a bit stiff as it sets, while retaining moistness underneath the outer layer that is exposed to the air.

Although I haven't often made frosting myself, I have tried several different types made by others, including buttercream frosting, cream cheese frosting, whipped cream frosting, and meringue, but they never seem to come close to the texture I like (as described above). So what kind of frosting should I be looking for to get that texture?

It would be a nice bonus to know what ingredients or preparation methods account for that texture, so I can look at a frosting recipe and make a good guess about whether it'll give me the kind of thing I want.
It sounds like you might be happy with Wilton Buttercream ... which is mostly whipped shortening and powdered sugar.  I don't have the recipe on me right now, but I did post a variation of the recipe to a related question a few years ago:  https://cooking.stackexchange.com/a/4869/67

Depending on how soft you make it (how much water you add) and how humid it is, after a bit of drying, it'll form a crust that you can use to your advantage (lay on some waxed paper, then press out any ridges).  You can then cover it so it won't dry out too much.

The important part of the process is a stand mixer, so you can leave it mixing for a really long time.