You need an account with active entitlement in order to download - if you have one try by logging here https://my.veritas.com
then select download which will move you to https://www.veritas.com/content/support/en_US/downloads
To help, there is no separate client package for Windows. There is the one package - server & client combined NetBacklup_<ver>_Win.zip
For older versions it used to be possible to extract from the above zip a client bundle, but these days the various cab files are shared, so it is not so simple.
This sadly changed starting with NBU 8.1.2.... They used to make the client and master/media server packages seperate but ever since they introduced NBU certs, the master/media package is now the same as client... which is not great because its a larger package... I wish it was still separated out... but Im guessing this is because of the cert requirements that its one and the same now. Once you start using the Deployment packages to push out client updates it no longer becomes an issue though because its all automated.