Technically, an official does not exist. Microsoft officially ended support for Windows Vista with Service Pack 2 as the final release.
However, the "Service Pack 3" keyword typically refers to either unofficial community-made update rollups or specific Server 2008 updates that can be adapted for Vista systems. 1. The Reality of Windows Vista SP3 download windows vista 64 bit service pack 3
Microsoft never released a third service pack for Vista. The operating system reached its final official version with Service Pack 2 (Build 6002). Technically, an official does not exist