I have seen fresh porcinis at the Alewife Whole Foods a few times. I cannot confirm whether they are always available, since I don't look every time I'm there. The last time I saw them the price was $49.99/lb I believe.
Saw some at Russo's in Watertown a week or two ago, worth giving them a call. Also saw and got some fresh Chinese shitakes which were awesome and different from the ones I'm used to. They usually have a great selection of non-standard mushrooms.