All the Splinterlands packs can be bought in tokenized form on hive-engine or even on the wax blockchain. Let's say you buy a chaos legion pack on tribaldex. You can then import the packs into the game.
For that you need to go to the "open" tab in your Splinterlands account.
For each series there is a symbol and at the bottom there is this kind of double coin. Click on it and another window will open.
On the left you will see your packs. You can then on the right import the packs into the game by setting the number, the source (hive-engine) and then click deposit. Now the cards will be in the game.
You can do the same the other way around and send your packs to hive-engine where you can trade them.
Hope this helps :-)