They’re part of the camera body, not the lens. Specifically, split-image and microprism aids are built into the focusing screen/viewfinder optical path.

If they were in the lens, they would affect the actual image recorded by the film or sensor, which is not what you want. These aids are meant to help your eye focus through the viewfinder only.

On SLRs and DSLRs, light passes through the lens and is then directed either to the viewfinder or to the sensor/film. So anything visible only in the finder must be in the body’s viewing system.

Whether you have these aids depends on the camera’s focusing screen design. Some cameras allow interchangeable focusing screens, some can be changed only by the manufacturer, and some do not support changing them at all.