If you mean first flight as in first flight of a new type, Boeing would have an article about it. If it's a first flight of an aircraft off the line, then it's no big deal. Airlines may also announce the first delivery of a new type in their fleet, but again, if it's just another of many, it's no big deal.
What exactly are you looking for. First flight of a model, or first flight of an airline or first flight on all aircraft? First of a model will be well publicized, first for an airline will be less publicized, but I could let people know....maybe. First for any aircraft would just be boring. All the same applies with deliveries.
Some people are like Slinkies. They bring a smile to your face when you push them down a flight of stairs.
I'm indeed looking for the "boring" info on first flights and deliveries of all aircraft. On my website http://www.planemad.net I offer production lists and therefore would like to have such information very quickly in order to update it very soon after a first flight or delivery took place. Airbus is no problem as I have a very reliable supplier but somebody for Boeing types is missing.