Is there another way to get candies for rarer Pokemon not relying on catching more of them?
Yesterday I caught a Dratini but as you guys know this will only give you 3 Dratini candy. So I was wondering, how am I supposed to evolve this Dratini when it is so diffucult to catch?
Capturing (or hatching) Pokemon of an evolution-chain (like Dratini-Dragonair-Dragonite) will give you candy for that evolution-chain. That is the only way to get candies.
Rare and more powerful Pokemon appear as your character level goes up, so you will slowly begin to find more Dratini and eventually gather enough candies to evolve it.