Make sure you uncheck the FM approved drivers and official results only boxes. I had the same problem when I was looking last week. After I did those two things I found a ton of scores. Also FM recently updated the ORB to allow 4890 to not be listed as a "generic GPU" so that should no longer be an issue and as far as I could tell the change seemed to be retroactive to scores that were already posted.
Here's a link to my overclocked HD4890 vantage score in case your interested
http://service.futuremark.com/compare?3dmv=1021570