I need a grommet badly!

Go to a glass shop or body shop and ask for calk strip that one would use to seal plastic sheeting to door behind door panel. It looks like a 1/8 inch sticky rope, and can be forced into and around antenna cable to seal out weather.

A second item that will work is sealing putty electricians use to seal an entrance cable where it enters an electric meter. It can be can be found at a big box store such as Lowes, looks like a little soft mushy gray brick about 4” x 2 ½” x ¾” wrapped in plastic.