Not an expert here by any means, but I think permission from the original creators might be a hurdle. I imagine they have the right to show the amv at Otakon for as long as they like, but actually uploading it somewhere outside of the convention could pose trouble for them, maybe? And if they can't contact the original creator to get their OK (since any contact info used in the 90s could very well be completely defunct now), they might not want to risk any issues.
That being said, the above comment about AMV.org is the right way to go. That website has been around a long time, and could