Which of the following is not a common site for metastatic calci
Metastatic calcification may occur widely throughout the body but principally affects.

Interstitial tissues of gastric mucosa
Kidneys
Lungs
Systemic arteries and
Pulmonary veins

The common feature of all these sites, which makes them prone to calcification is that they can lose acid and therefore they have an internal alkaline component favourable for metastatic calcification.
Also, know

Metastatic calcification occurs in normal tissues whenever there is hypercalcemia.
Usually, deposition of the calcium does not cause any clinical dysfunction but sometimes massive deposition in the lung may produce abnormality and in kidneys may produce nephrocalcinosis.
Gastric mucosa
Kidney
Lung
Parathyroid