Searching the city for that one obscure beer you crave can be like trying to find a needle in a haystack, in that both of those endeavors end with you giving up and drinking Schlitz in a barn. For a spot that's more than likely to have what you need: Beer Wine & Co.
From the Bethesda crew that brought you Food Wine & Co. and are as awesome at stocking shelves as they are bad at thinking of creative names, Beer Wine sells just that, with 440 bottles of vino and 340 of suds lined up on endless maple and birch racks, including rarities like:
Baladin: This Italian beer house makes only 2-3k cases a year of their Super (a Belgian strong ale), and are known for playing music to the beer to during the yeast-straining process.
Brewer's Art: Sending BW&C some of their Abbey-style Resurrection, this tiny Baltimore brewery is almost never seen outside of B-town, much like anyone who goes into Baltimore alone at night.
San Lorenzo, Pecorino: This Italian wine's one of the most rarely produced in the world due it being fermented from a grape that nearly went extinct -- explain that to your date over a glass, and you won't even have to whip out the cheese.
Aecht Schlenkerla: A Marzen (German-style lager), this brew's fermented with oak chips, which gives it a smoky taste and very smoky smell (like a "charred hot dog"!).
Build Your Own Six-Pack: While not technically a rare beer, it is awesome, and is also what Matthew McConaughey yells at paparazzi when he gets fed up.
They'll also be doing copious tastings for both wine and beer, and stock non-liquid goodness like all kinds of charcuterie, cheeses, jams, chocolates, and baguettes: a full line of goods, meaning the next time you want to have a party not in a haystack, this place will totally bail you out.