Yeah, I had to go to gamestop to pre order my copy and even then they said that the only copy they had for the 360 was the legendary edition. You may have to go to you're local video game store and just pre order the one they have available.
As far as has been stated, it will be available on 360. We are jsut waiting on Bungie to release the license for us to get it on 360, once that happens it will be up on the marketplace. Even the destiny website doesn't have the option for 360 yet.