You might try calling Aphrodite in Bailey's crossroads and asking. They're a door or two down from Rabieng (not easily visible from Rt. 7) in the little plaza adjacent to Lucky 3.
Mediterranean Bakery in Alexandria is also worth a phone call.
I didn't realize you could get preserved lemons at Whole Foods - will have to check. Last April, after a long search to no avail in the area, I bought some in London while on a business trip. I have since made some, but it takes a long time!