Yes, gather is not available for SQL yet. There is dedicated issue here - https://github.com/tidyverse/tidyr/issues/379. There is also a comment by iangow that he references that implements it using already existing verbs in dplyr.
One alternative can be replyr - https://github.com/WinVector/replyr. I've never used it myself, but at least following the blog-posts of the author I've got an impression that it might solve your problem with gather.