I need to know the name of this plant and where can i buy one
That is an Orbea, or Carrion Flower.
As far as where to purchase- We do not offer such information. I would check local sources, or online resources, such as Amazon, Etsy, Ebay.
Here is an article with more information on the plant: https://www.gardeningknowhow.com/ornamental/cacti-succulents/starfish-flower/growing-starfish-flowers.htm