It is very easy to walk into any pharmacy and buy multivitamins which contain calcium, calcium+ vitamin D supplements or just plain calcium supplements.
The question is why would you do this? Many people do despite the lack of any good convincing reason other than media selling. People continue to be persuaded by media hype rather than follow scientific studies and evidence.
However, if you have actually been shown to have low bone mineral density (osteopenia or osteoporosis) or are at risk of bone fracture such as the elderly, then your doctor may prescribe calcium supplements such as calcium/vitamin D. This is an accepted medical intervention designed to prevent bone fracture. Taking calcium in the absence of any such problem is the controversial point.