How do I get the latest logrotate, which isn't yet in the apt repositories?

One solution that I have used before is to just download the .deb package from a future release. For logrotate, that would be this link. From here, just select the architecture, and then the mirror to download from.

You can install it by using dpkg -i. If you are concerned about doing this, you can extract the contents into a temporary directory and see if anything looks like it might conflict with something else. For example: dpkg-deb --extract <deb file>.

When you finally decide to install it, if there are dependencies, it will warn you about them. (Of course, there is a list at the link above, as well.) If the dependencies are already satisfied, then you're done. If they are not, then you can decide whether you should manually download those or if you've gone too far and should stop. A dependency that many other programs rely on will cause you more problems down the road.

Keep in mind that when you upgrade your system, you might want to remove it and put the old version back and let the system upgrade it itself.

I have done the above previously with programs that had very few (usually no) dependencies.

Thanks to comments above, here's an updated list:

• upgrade to an interim non-LTS release (which has the new version)
• wait for next LTS
• official PPA (if one exists)
• ask (on launchpad) for it to be backported
• install .deb package
• compile from source

That should be applicable for any package, not just logrotate.