How often do legendary cards appear in the shop?

As a keen player of the game, I'm always on the lookout for those elusive legendary cards in the shop. But it seems like they're more difficult to find than a needle in a haystack! So, I'm curious to know - just how often do these coveted cards actually show up for purchase? Is there a specific rotation or frequency to their appearance, or is it truly random? My hopes are that there's a pattern or trick to increase my chances of acquiring one, but I'm afraid the answer might just be a roll of the dice. Either way, I'm eager to find out more and perhaps improve my chances of adding a legendary to my deck.