I would imagine CoStar has this market cornered. If a developer or site selection professional were out there searching for such a facility, CoStar would almost definitely be their first stop.
If you were determined to develop something along this lines that highlighted a bit more what the communities were hoping to see developed on these locations, I could see it being done at an MSA/Regional level and might be a worth while discussion to have with your regional chamber of commerce (if such a chamber exists near you) or other regional entity. The large regional chambers often function as much more of an economic development agency than their smaller local counterparts and they do draw website visits from the site selection community.
A national level website highlighting vacant big boxes and development opportunities would be too difficult to maintain the information in and make sure everything is current, especially the contact info for each property as vacant retail properties can often change ownership and property managers through various transactions and court proceedings that would be exceedingly difficult to track.