The existence of this query highlights a failure of the "Streaming Wars" model. While content is abundant, it is siloed.
However, this creates a technical paradox. Many of the Serbian/Croatian dubs were recorded and broadcast in standard definition (480i or 576i). Finding these specific audio tracks in "extra quality" (1080p/4K) often requires hybrid files where fan communities splice the old SD audio over HD video, or upscale DVDs. The user is asking for a product that technically may not exist in an official capacity, driving them to sophisticated file-sharing communities rather than simple streaming sites.