Because I used crystal plates, I wanted a little color in the napkins. I went to a few local stores, but most of the offerings were limited. Online I found a plethora of cocktail napkins.
I landed at ShopCocktailNapkins.com. I know, the name seems a little, "This can't be for real," but it is. It's part of a larger entertaining supply company called Giftaria. They have web sites that are very specific to certain party needs, like baseball and elections, and in this case, cocktail napkins.
To keep the theme of the black/white damask, I found the Damask Black & White Beverage Napkin. And for the purple color, I found some Aubergine napkins. (They have since sold out.)