Aero In Stock is where I got mine.
http://www.aeroinstock.com/
They have the Champion M-2375 Grommet Plate Ignition Lead 2 Hole 1/4 Dia and the M-2375 is the correct size for Slick Mag ignitions leads.
Aircraft Spruce also has "ENGINE BAFFLE IGNITION WIRE SEALS". The two wire p/N 07-01014 5MM WIRE SEAL TWO-WIRE fits .375 diameter ignition leads.