I typically Google what I am looking for, like scx24 stl file. Google does a lot better job than the 3d site search engines. Plus, there are some sites out there where users sell their stl files for very reasonable prices. Google finds some cooler stuff because of those random sites out there.
I don't typically print other oeople's stuff. I can't tell you how many times I have, only to find out they modeled something wrong.
My advice is download the free version of Fusion 360 and watch some YT vids on how to use it. Like this 3 part series