You might be searching for "AppSync Unified repo repack" because of one of three scenarios:
MASTG-TOOL-0127: AppSync Unified - OWASP Mobile Application Security
If you cannot see AppSync Unified after adding the official repository, it likely means you have another, conflicting repository added that is also hosting a copy of the tweak under the same package ID. You may need to remove the conflicting repo to resolve this.