DC area: resources/realtor for unique property search?

[John Fabros]

My family (myself, brother's family, parents, in-laws) is looking to create a multi-unit, possibly mixed-use compound in the greater DC area. Coming from the Midwest, we had been hoping to find an old industrial building or warehouse ideally on a waterway, for easy conversion (5000+ sf base area, 20+ ft height or multiple floors, drive-up/drive-in access), but are clearly very late to the party. Aside from the overall high price levels which will probably be insurmountable regardless, there seems to be a very narrow market for the size area we're looking for. We're willing to tackle what others might consider scary, but tools like Loopnet/Craigslist are either not effective in finding what we're after or what we're after simply doesn't exist anymore. Any recommendations would be greatly appreciated.