Correct AC grommet

[PbFut]

On my 72, there is a odd sized grommet hole for the ac cable in the firewall above the evaporator box. I think it is 7/8". It is a single hole grommet with only the control cable passing through. The AC vacuum and wires pass through a hole at the tunnel. The firewall hole for this cable grommet is larger than the 3/4" holes used for single wire pass like the tach and aux battery. But it is smaller than the holes used for oil pressure or windshield washer tube's. Does anyone know a source for this odd sized grommet?