Intersections will be in the roads tab, the 5th tab (2/4/6 lane, motorway & intersection), same with roundabouts.
A 'large ploppable residential area with roads and such' sounds more like a save game tbh. I did the same the other day liking the look of a fancy looking airport all pre-built, couldnt find it then realised something that size couldnt possibly be a ploppable, iirc the largest size we can plop is 12x16/16x12. Its possible it could be in the interchanges tab if its small enough, but im not sure if its just me but none of the road related stuff has been particularly great for plopping into an existing scene. It doesnt want to attach to existing features. I built a mini roundabout, the access roads i included wont lock to the roads already placed, so you have to delete it or plop it just away and road onto it. So a stencil style ploppable wouldnt work either. I do hope they'll fix that, cos it magnetises/snaps to road, but never lets me place it.
It's this thing.