Learn Swedish: Vi försöker hitta en likadan souvenir. - We are trying to find an identical souvenir.

Because it describes souvenir, which is an en-word (en souvenir). If you were describing an ett-word, like ett bord (a table), you would use ett likadant bord. For plural words, you would use the plural form likadana.

What is the difference between looking for samma souvenir and en likadan souvenir?

Samma means the exact same physical object. You would say samma if you lost a specific souvenir and are trying to find that exact one. En likadan means "an identical one" or "one of the same kind." You use it when you want to buy a second souvenir that looks exactly like the first one.

The English translation says "an identical", so why not use the Swedish word identisk?

While en identisk souvenir is grammatically correct, identisk sounds quite formal or scientific in Swedish. For everyday situations, like shopping for a matching item, likadan is the most natural and common word to use.

Why isn't there an att (to) before the verb hitta?