Where do you buy cards in Splinterlands?

Excuse me, could you please clarify where exactly one can purchase cards for the game Splinterlands? I've been hearing a lot about it lately and am interested in trying it out, but I'm not sure where to start. Are there specific online marketplaces or stores that specialize in selling these cards? Or are they perhaps available through the game's official website or a third-party vendor? I'd appreciate any guidance you can provide on this matter.