After the D rest can i rack to keg to do the lagering phase? or should it stay in the fermenter for some more time?
Lagers are boring. Really boring. Expect a slow fermentation. Be patient.
A diacetyl rest should be preformed at about 5 points from terminal gravity. So somewhere around 1.017.
As far as a commercial example- I have no clue in Atlanta. In the Chicago area we have a large liquor store chain called Binny's. They have 12 German Helles type beers in stock.
Google tells me they might carry Weihenstephaner Original Premium Lager Bier at The Juice Box.