Certified GKH Gardening Expert
We do not recommend specific places to purchase, but you can check Amazon, Etsy, or Ebay. These places will often have what you are looking for.
As for care indoors... They are very light hungry. You will need very bright horticultural light. Window light will not be enough to keep it healthy. I would recommend 200 watts or more. Other than that, they will be cared for as you would in container outdoors. Just make sure that you have PLENTY of light.
Just a little note: These plants are VERY TOXIC. It only takes a few small bits to be fatal. Make sure that no children or pets can have access to this.