Epic cards, like Prince, can only be requested on Sundays.
On Epic Sundays, you are allowed to request Epic cards once. The number of Epics you can request at one time is equal to the number of Rares you can request.
Legendaries cannot be requested.
You will receive 1 XP and 5 Gold for each Common card donated or 10 XP and 50 Gold for each Rare card donated. For every Epic card donated, you get 10 XP and 500 Gold.
Clan Members can request Common, or Rare cards once every 7 hours with Epics available on Sunday. Cards received depend on your Arena level and card class:
Goblin Stadium
Donations – 1 Common or 1 Rare
Requests – 10 Commons or 1 Rare
Bone Pit
Donations – 2 Commons or 1 Rare
Requests - 10 Commons or 1 Rare
Barbarian Bowl
Donations – 2 Commons or 1 Rare
Requests – 10 Commons or 1 Rare
P.E.K.K.A.’s Playhouse
Donations – 4 Commons or 1 Rare
Requests – 20 Commons or 2 Rares
Spell Valley
Donations – 4 Commons or 1 Rare
Requests – 20 commons or 2 Rares
Builder’s Workshop
Donations – 4 Commons or 1 Rare
Requests – 20 Commons or 2 Rares
Royal Arena
Donations – 6 Commons or 1 Rare
Requests – 30 Commons or 3 Rares
Frozen Peak
Donations – 6 Commons or 1 Rare
Requests – 30 Commons or 3 Rares
Jungle Arena
Donations – 6 Commons or 1 Rare
Requests – 30 Commons or 3 Rares
Hog Mountain
Donations – 8 Commons or 1 Rare
Requests – 40 Commons or 4 Rares.
Electro Valley
Donations – 8 Commons or 1 Rare
Requests – 40 Commons or 4 Rares.
Legendary Arena
Donations – 8 Commons or 1 Rare
Requests – 40 Commons or 4 Rares.
You cannot receive entirely new cards by request. It’s necessary to first discover them through Chests.
Donating cards also gives you Gold and XP:
Common > +5 Gold & 1 XP
Rare > +50 Gold & 5 XP
Best Answer
There are only a few ways to get them, but it's possible. The following are based on being in Arena 9:
Opening Super Magical Chests - Super magical chests are the highest quality chest in Clash Royale. They can be obtained by buying them for 4600 gems in the store, or getting a very lucky drop at the end of a battle.
Buying them from the shop - While rare, they will sometimes appear in the shop and costs 40,000 gold. This is actually a much better deal than the Super Magical chests because 40,000 gold is about 2,000 gems.
Other than that, there's not much to do. There is a better chance to get a Super magical chest drop as the higher your rank is, so just keep trying to climb and refine your deck to the meta.