There are a whole host of veggies and fruits available in Luanda, not all the time though, but if you shop at a few different shops in one day you might be surprised. Example, Jumbo, Intermarket and Casas dos Frescos(Very Expensive), Kero.
Casa dos Frescos, 2 in Luanda City that I know off, Kero and Shoprite in Tella Tona. Intermarket on the Marginal above President Hotel and off course Jumbo in the city.
Go during the week if you want to get the biggest variety since people buy the shops empty over the weekends, get a driver to take you to these shops. The drivers know where most of these shops are.
Many shops now like Shoprite and Intermarket already sells seads for spices and veggies, check it first.
Cheers
Le Roy