One place you might try is here: http://www.trainzonline.nl/pages/downloads
Each time I go to a new Trainz site, I check the "links" pages and eventually gets me to nearly anything I need.
You may try saving the sites you go to most as "Favorites" and find the Download button or tab once you're there.
Many "clicking" efforts have helped me in these 14 years.
Good Luck.