Not sure rank 2 chickens are necessary, as it's rather easy to rank up commons to rank 2. I mean, what else are you going to do with summons you get with Mystery Shards?

They're very rare. They were in a fusion warmup last year, but since I started at the beginning of 2021 I can't recall seeing them come up all that often. 

But yeah, just use your other rank 2 champs at level 1, like Occams said more or less. 

You can get them at the Clan Shop for 100 Clan Coins, but it's hardly worth it.

Would not buy there, definitely. Much, much better uses for your clan gold.