I have generated gen3 refcat ingest index files for our primary reference catalogs (ps1, sdss-dr9, gaia-dr2) on lsst-devl at /datasets/refcats/htm/v1. These .ecsv files serve as input to the butler ingest-files command described in section 4 of How to generate an LSST reference catalog — LSST Science Pipelines. Our existing /repo/main repository already has these refcats, but this should simplify future butler repository creation.
Others can use these files to easily ingest these refcats into their own gen3 butler repositories (e.g. at the summit); if you are doing so on a system other than lsst-devl, you will need to change the paths in the files (with e.g. sed) to where you you put the HTM indexed files.
Note that if you want to ingest the sdss-dr9 refcat into a gen3 repo, your local directory and the entries in the .ecsv file need to be renamed to replace the - (dash) with _ (underscore), due to - not being allowed in dataset type names in gen3.