Retroactively download all of a user-group messages to my mailbox

Question

I'm going to want to search in some user-group archives (https://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/) for a good while. Unfortunately, their UI completely sucks and makes searching extremely hard (maybe I could also do it with Google).

My experience with Gmail's search algorithm is quite good, so I was wondering whether it would be possible to somehow leverage it.

I know these groups allow anyone to just register and then get / send emails in their personal mail. And that made me wonder: is there any possibility of having all their old emails get downloaded by Gmail (or any other email service provider you can think of), as to make searching the messages a breeze?

Thanks