Not true. There are DOZENS of third-party sites around the world that host Trainz content, and a relatively small sample is at Trainzland, mostly older assets. There is a thread in the General forum for posting missing asset KUIDs, where some of the rest of us may be able to help you find them, although these days it seems to be about a 50-50 shot.
You CAN sort by KUID number in CM and DLS. In your CM, right-click on the column labels at the top and select "Insert Column". You will find several columns you can add to help your searches. One of them is "Asset ID" Once you have this column added, you can click on it to sort by KUID. I do it a lot to help folks that post in the missing KUIDs thread in order to see if I have it and maybe where I got it.
At any rate, you can't delete unknown assets, because you don't have them anyway. What you want to delete are the REFERENCES to unknown assets.
If you want to delete (references to) a missing asset, there are two ways. If it is a dependency for a route, load the route in Surveyor and then locate "Delete Missing Assets" in the menu. Note that when you do this you will have to save a copy of the route under your own ID. If there are sessions, you will then have to point them at your map instead of the original (NOTE: you may also want to check the description of the route to see if it contains links for dependencies, or if it names the site or contact info for the route creator, and if it is a freeware route, see if there is a thread for the route under the Freeware forum, as this may have links to dependencies, or you can post asking about them).
If the dependency is for a regular asset, like a hornsound or an enginespec for a loco, you can replace it in the config.txt file with a suitable substitute. Sometimes by editing the config.txt file you can determine what the missing KUID is by finding it in the file and seeing what kind of tag it is. (If you try to use this method on routes, be aware that it will work temporarily, but if you ever do a DBR Trainz will notice it still has an asset missing from the route and will again report the route as missing dependencies.)
