The following internet links can be useful for ALMA users requiring an ephemeris.
https://ssd.jpl.nasa.gov/horizons/app.html: Direct link to the HORIZONS web interface. This is a very useful link as, if an ephemeris has previously been generated using the web browser, it will bring up the inputs that were last used.
https://ssd.jpl.nasa.gov/horizons: HORIZONS web page (web interface link can be found here, in addition to multiple formats for documentation).