Looking for Lefse--DC/Alexandria
There used to be a little place (City Market, I think it was called) in Arlington that carried it, but I'm pretty sure they're closed now. IKEA sometimes carries it, although I would probably try to call them first to check to see if they have it. You could also call one of the Russian Gourmet stores (there's one in Alexandria on Slaters Ln), as they sometimes have Scandinavian items, or maybe even call Domku and ask them if they know where to get some.
As a last resort, if you left now, you could probably make it to North Dakota by the end of the day. :)