Can be bought at most places. Target. Best buy. Where ever. It is just a can of air under pressure used for cleaning electronics. Such as keyboards etc. Go to a store ask for a can of air. View attachment 18500
hope this isn't too late, but just be careful to not turn the can on it's side or upside down when you use it. A not so friendly blast of very cold gas will come out, not just 'air'.
But you would have to spray it for a few seconds like that for it to really do anything.
DO NOT USE COMPRESSED AIR! Lol I'm serious though. Air has humidity in it and when you blast the phone u may very well blast h2o into. And rubber alcohol will definitely take the oleo-phobic coating off the screen. Apple even says to not even use windex. Take a piece of paper edge or a candy rapper to pick it out don't mess with that beautiful white phone.