African Roller and Asian Kingfisher are not endangered, nor threatened. In fact, they are very abundant species. And as for using the feathers of a bird that has died in an aviary, there is no endangering of anything from this. It does, however, lighten a person's bank account by quite a bit for these rare bird skins from an aviary. And many aviaries sell the skins of theie dead birds to help pay the bills to keep the other birds fed and healthy.
That said, Natrix you are correct, there is no need to use the feathers from rare birds. Jungle Cock is not a rare bird and it is also raised domestically, Blue-eared Pheasant (and its cousins the White-eared and Brown-eared) are raised domestically and readily available (although a tad high is price for some people), Argus Pheasant is another domestically raised bird, and Kori Bustard is another one that is raised domestically (unfortunately in my opinion the feathers are priced way too high because there are those who will pay whatever is being asked to get the feather). In other words, not all the rare bird feathers are endangering the birds.
One can tie a very nice classic full-dressed featherwing without using any exotic feathers at all that only someone who is very knowledgeable about the original feathers would know was tied with substitutes.