Where is the very first place that new music is accessible to the public????

There's no one answer, it depends on label, artist, etc, however there are commonly music videos released for singles before the rest of the album onto youtube. Most of the time everything else will be released on the same day, maybe only with hours in between, onto spotify, physical copies, etc.

Why?

I'm not entirely sure about this, but I think some artist release some of their stuff on their Soundcloud before the label does.

I remember when Tool leaked "The Pot" way before 10,000 Days was finished.

When I was still in the biz, it went radio, single via video, single for sale via iTunes/physical, then an official album release date where iTunes and stores got it at the same time. Its not a rule, but sony, who distributed my band's label, did it that way.

The interwebs!!!!

for hip hop, http://virdiko.com/

not all but a good majority of it (even some mainstream b4 it touches social media or itunes), good dj pool for getting the jump on new releases to be the first remix or isolate vocals to catch that initial wave of "web traffic" to gain notoriety

another alternative http://djservicepack.com/

I don't know about any other dj pool's for other genres.

I do know tho there are certain publicists / pr people you can get in touch with that exclusively send stuff out to companies that film commercials and what not b4 its released, thats a circle you have to / can brown nose your way into tho.

(another thing to look for remix contests on beatport, u can usually find hq wav files of tracks tht are un-released including their stems also in wav format. this route really only applies to techno and edm tho... mostly*)

I'm not entirely sure about this, but I think some artist release some of their stuff on their Soundcloud before the label does.

I second this