Colandro's on Government Street in BR has singles of European beers. Not sure if they have any lambics, but the whole top shelf is single bottles. I live a few blocks from there and usually stop in a couple times a week. I'll let you know.
Edit: I forgot to add that the lady who works the wine/liquore/beer section is extremely nice and she will order anything you like. Also, their prices aren't the best, but if you compare it to shipping from someplace online then it usually breaks even.