I don't know that I am particularly more experienced than you, but sounds like we have a similar philosophy. I don't know about Vanguard, but in Fidelity there is a specific "New Issues" section for all bonds, as well as a specific "New Issues" area under each bond type....such that if you go into the default bond search (which is secondary), you wouldn't see them.
I definitely find value in saving on the secondary commissions by buying new issues. Annoying fees aside, often many of the new issues never even end up available in secondary.
If you are limited to one broker, there isn't much use (IMO) of trying to look up all the new issues because different brokers get different offerings. But you can look up on each GSE webpage (ex.
https://www.fhlb-of.com/ofweb_userWeb/pageBuilder/new-bond-issues-48)