Yes
Yup. They have a pretty decent selection too. And as has been said, you can buy d20s singularly or in the full sets.
They also sell each type of dice individually
The sets range from $5 to $15 depending how fancy you want the dice to be
Yes they do. You can buy individuals, or they sell dice sets.
Yes, 20 sided die are sold individually and a variety of dice sets are sold at Dragon's Keep.
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