I think Russell said he'd asked something similar and been refused, have to go check on that... I'm not sure that proves anything, though. If I were in the press office of any US Government body then I'd probably ignore such requests, either, because if you don't they'd never end.
If someone called and asked if they'd matched components, for instance, and they said yes, then it wouldn't end there. They'd just be accused of lying, asked to prove it.
Next up might come pictures of a warehouse full of wreckage. But how's anyone going to prove it's not been faked? Even if you personally visited, looked around, how could you know it really was from a particular flight?
Let's suppose you got some serial numbers, and they turned out to match parts on some audit trail that lead back to Flight 77. That audit trail would just be pieces of paper and computer records, something that I can't imagine would be difficult to fake, and so not everyone would believe those, either.
In other words, if you're someone who already believes the Government has faked/ lied about the retrieval and identification of the passengers from the sites, and the black boxes, then I think you'll probably go on making exactly the same "hoax" and "fake" and "lies" accusations against any other evidence that might appear. Doesn't mean I might not like to see it too, I just don't think any of it will end the argument, not now, not ever.