You can purchase Spawners in the game Bank - tap onto the icon with Sapphires at the top right corner, switch to Special, then to Protection tab.
Purchased Spawners are added to the Vault. Upon claiming they appear in the tab Furniture in the Construction menu. Open it and place your Spawners in the free slots in your Shelter.
N.B. Spawners activate automatically as soon as a raider enters your Shelter.