Greetings cards are not a big thing here, although there are Hallmark shops in SD. The Diamond Mall branch closed down recently, so try one of the other big malls. Toy shops, book shops like Cuesta and Thesaurus and shops selling gift type items may have a rack of cards, but the selection is usually quite limited.
The large supermarkets (Nacional, Bravo, Pola, Carrefour) sell a reasonable range of spices, and there are specialist deli-type places like Omaha Steaks and L'Epiciere de l'Orient on Plaza Paseo de la Churchill (Churchill esq. Pastoriza). In addition, you will find good Chinese supermarkets on Romulo Betancourt and in Santo Domingo's own 'Chinatown' in and around Av. Duarte/Benito Gonzalez.
Hope this helps!
Chiri