They pulled all the betas and everything older than 4.7.3.
This is something I expected and you could say I suggested it.
For now, you can get b20 from me until it expires. It has 7 days left.
http://0.0.0.0/BSTEST510b20.exe [Expired, link is now dead.]
There are plenty out there shared on the gnet too, so the historical collection is safe.