Well if you want royalty free stuff (meaning you can use it about anywhere including in something you’re selling) a good place to start is with a sound effects package. Sony makes a great one they advertise for use with Vegas (though you can use it anywhere). https://www.sonymediasoftware.com/loop_libraries/ShowLoop.asp?SPID=399
You can buy all 10 volumes on that page. Or they have it broken down into two smaller packages that are cheaper. There’s two links on that page I gave you. They also have samples. These are way high-quality.
If you’re looking for free to use for just personal stuff (non-commercial) there’s a bunch of varried web resources. A good post on this on another forum can be found here: https://fxhome.com/forums/viewtopic.php?t=24147&sid= (Click the “Sound/Music” link under “Contents”)
–the Fiddler