Fork, use your fork, send a pull request. Almost every rails upgrade I make forks and send patches on gems that I need that I forgot about. I get good responsiveness and merge rates. Most of the time a gem needs to be able to support multiple rails versions, so in that case I usually send pull request setting up the Appraisal gem to test for appropriate compatibility.
You can't do them all, but you can certainly pitch in and submit patches. Outside rspec-related gems, upgrading usually isn't that hard.