Hey guys! Welcome to the world of scanning, internet scanning, and radioreference.com.
I am not sure if you realize it, but all of the feeds that you see posted on the site are contributions from folks like you and me. They have scanners at their homes and they stream the audio so that folks can listen online vs. investing in a scanner. If you find a stream that you like, ask the owner of the stream if he/she would mind adding a channel or talk group to their scan list. It is completely up to the scanner owner as to what they place in their scan lists and ultimately upoad via their audio stream.
I hope that this helps!