Is it possible to get a card from a previous arena? [duplicate]

Chests can contain loot from previous arenas, I myself opened a Giant Chest in arena 4 that contained 100 (?!?) skeleton cards from arena 2.

In addition to chests, the shop will rotate through cards from older arenas as well. Once you have at least one, you can ask for more from your clanmates as long as it isn't Epic or Legendary.

Some folks try to claim that you can get old arena cards faster at lower arena ranks, (since there are fewer choices for chests to give you) but this is a myth. My partner EBongo debunked this 'exploit' with his mad math skillz, and I took his epic formulae and turned it into a web based card upgrade calculator. You can use the calculator to figure out how long you'll need to grind to upgrade a given card at your current arena rank.