One poster reported seeing them in the San Pedro branch of Jumbo recently, so you could try in the MegaCentro (Zona Oriental) or in Nacional supermarkets (same parent company as Jumbo). Problem is that these things come and go, they don't always restock immediately, and as Easter eggs are not part of the DR tradition it doesn't mean they will have them at this time of year in particular. If you don't find Kinder eggs, try the main chocolate section for those bags of solid chocolate eggs in coloured foil - I've seen them on sale from time to time and they are good for egg hunts.