Where to find sps in Splinterlands?

Could you please clarify for me where exactly I can locate the sps, or special power stones, within the Splinterlands game? I've been trying to enhance my deck and have heard that sps are crucial for this process, but I'm having trouble pinpointing their exact location within the game. Are they earned through gameplay, or can they be found or purchased in a specific area of the Splinterlands platform? Any guidance you can provide would be greatly appreciated.