Finding Housing close together is sometimes more luck and patience. I've managed 4 in one spot as I placed one and others fell around me. But it was years in the doing! Then I gave them all away and moved. ha!
FCB's fishmarket and MOA both have runebooks to empty spots, NOW these are done by volunteers so updating is sometimes spotty and based on who is out roaming where. They might get you a start.
Roam around with both runes and a house placement tool and just look at the terrain, housing etc. Should be able to use the tool to view a plot and NOT actually place. Don't want to condemn any current houses.
The other thing is to talk to folks at the auction houses, vendors who own houses if you catch them at their home. Sometimes you'll find someone who knows someone who wants to dump or unload several houses and close a bunch of accounts. It's happening a lot more these days.... player who once held 5 to 10 or more accounts with houses and storage bringing their account totals down to 2-3.
Those are the best tips I can give you.
