MadReferee's correct. Not sure where my head was (don't answer that).
In short what it means is that up until 2010 manufacturers can still make and sell LSD. But they can only make 20% of the diesel they make as LSD. The other 80% must be ULSD. At the 2010 deadline they must produce 100% ULSD.
Your also spot on about the retailers. Most gas/diesel stations only have one diesel tank so they will only sell ULSD. Larger stations like truck stops will probably have both LSD and ULSD pumps since they have more than one inground tank.