Where can I buy Suica no Penguin goods?

I've heard there's a JR East store somewhere in Tokyo Station selling Suicaのペンギン goods and other train-related items, but not sure where! Would anyone have more info? Or know of other stores?

I've also stumbled across small sections of merch at various NewDays shops in the past… anyone happen to have ideas as to which ones might have good selections? (I know there's always JRE MALL online too but shipping is expensive and they have limited selections and only new releases).

If it helps, I'm specifically looking for a keychain plushie of the penguin, but open to other stuff too!