Because the official search engine is notoriously slow, community members have created scraping tools and websites.
The Download Station is Auran/N3V Games' official server. It contains over 500,000 assets. A top-tier search here requires using the White Pages.
How to perform a high-level KUID search on the DLS:
The "Top" Hack: Use the "Download Helper" feature. If you have a route with 100 missing assets, don't search one by one. Copy the entire list of missing KUIDs from the in-game validation tool, paste them into the DLS "Bulk Download" text box, and let the website queue them all for your Content Manager.
Once you have the basics down, these power-user strategies will cement your status as a KUID search master.