There's also only one of them, inserted randomly into one of the Kingdom Card piles at the beginning of the game. And when you play it, you return it to your hand.
In a similar vein to that idea (of having only one of that card, shuffled randomly):
Anonymous Benefactor - Cost $3 - Victory
Discard any number of cards. +$5, +1 Buy per card discarded.
During your Clean-up phase, shuffle this into a Supply pile chosen by the player to your left.
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Setup: Shuffle this card into the Estate Supply pile.
Or an even better one (I wonder if this one is actually even broken):
Allegiance Loss - Cost $4 - Action / Attack
Each other player reveals his hand. If the Allegiance card is revealed, shuffle it into a Supply pile that you choose.
Allegiance - Cost $0 - Victory
50 VP
When you trash this, shuffle it into a Supply pile that you choose.
In games using this, there are 10 Allegiance Loss cards (their own Supply pile), as well as an Allegiance card that is shuffled into the Estates.