I pretty much follow the same procedure Euphod outlined, but in a slightly different order: I start (and often end) with Google, and because Google knows about these forums, I skip searching the forums directly. If I don't find anything there, I open the content managers, sort by author ID in ascending order (this is the number between the first and second colon of the KUID), and see if I can find the name associated with the KUID from there, it's a matter of association to see what Third party site the author is associated with, and start the hunt there. This is especially useful when the 3rd party site is not in an English speaking country. Also, while Euphod is correct about the utility of Trainz Pro Routes (TPR), that is not the only 3rd party site with content. HP Trainz, Blue Sky Interactive, and USLW, just to name the first four sites to come to mind, also have content, as you've found.
In fact, sometimes, when I don't feel like running a train, and am not feeling sociable enough to participate in the forums, it's worth the time invested just to navigate to different 3rd party sites, and see what is available.
ns