I recently moved from Leap to Tumbeweed and there are a few packages that I miss.
Where should I request them to be included in the official repos?
To be added to official repo package needs an active maintainer. If nobody bothered to submit package for inclusion in Factory so far, it is rather unlikely that maintainer emerges out of nowhere just because someone “reported” it.
Packages missing in Tumbleweed are most likely packages that no more build against newer software in Tumbleweed. So they must be fixed, not reported.