The easiest and quickest way ?
Go to the Assetto Corsa/Mods section ..... click on the Search button at the top and right ...
Just type the name of the track or car you're looking for ..... click on the choice where you see "Everywhere" and choose"this forum".
Among the received answers look for the ones beginning by "Tracks" for locations and "Cars" for car mods and you'll come at the precise wished place according to what you're looking for.
And still more precise of course when you're on the Tracks section or Cars section according to what you mean to find.
Jean-Pierre is absolutely right and it’s a method I use, but I also often find using Google almost as good, eg “race department asseto corsa tracks Le Mans la Sartre” or whatever in the Google search bar. It can be a quick solution