That’s great that you’d like to pick it up. It does look like it’s gone unmaintained. Please try some public communications with them such as opening a ticket on the repository.
As per the distributed nature of ROS development there is not centralized control of the code so if you cannot reach the owners or maintainers there’s no one else who can give you access. But since it’s an open source project you can fork it and continue development.
I’ve also tried reached out to them directly to see if I can get a response, and can confirm that all the maintainers emails bounced as undeliverable. I’ve reached out a few other ways but suspect that a response is unlikely.
To that end I’d suggest you go ahead and make your own fork to work on. And if there continues to be no response from the maintainers for a couple weeks you make releases using the same name from your fork.