There are no sites like the one you're talking about in the world. There's only the original, which is the N3V-Auran Download Station (DLS).
This Eastern European site hosts both free and paid content without the authors' permission. It's a kind of DLS, but without the authors' permission, like a pirate site.
If you want to download from that site, you need to register and provide an email address.
Do you think it's a good idea to give your email address to an Eastern European website?
As for searching for kuids, it's a never-ending task, as there are hundreds of websites around the world, and what's worse, many of them are closing, and this has been happening since the beginning of Trainz.
When an author uploads their content to the DLS, in theory they are the author and owner, but in practice, the rights to those objects belong to N3V-Auran, and they can create paid content with them. This is why some authors don't upload their content to the DLS, preferring to pay for a website and maintain it that way. The problem arises over time when paying monthly or yearly for website maintenance, as well as potential health problems, lead some sites to be abandoned.
These circumstances lead to unknown kuids. A few years ago, a route creator downloaded content from one of these defunct websites, incorporated it into a route, and when he finished it and uploaded
Royal Dream APK it to the DLS, problems arise for those who download these routes.
I've been downloading from trainz websites around the world for 20 years, and I assure you I have several thousand unknown kuids. You'll almost never be able to get all the unknown kuids.