Is it possible you're referring to a "Grease END Plate" (not a grease "and" plate)????? If so, all of the Model A parts vendors carry them. It is most commonly referred to as an End Plate Tube with a Ford Part Number A3568T in most catalogs. The steering box has a diamond shaped plate on the bottom with a "***" on either side where the light switch bale (wire keeper) is attached. There is a 7/16 hole in the middle of the plate to allow the Light Switch/Horn Rod to pass through. The End Plate Tube is a modified plate with a tube through the center hole. This tube goes up all the way through the steering box and around the horn rod to divert any steering box lube from leaking out the hole in the plate. This, along with a new gasket for the plate, will stop lubricant from leaking out the bottom of the steering box.
Without further dismantling the steering box itself, other vendors also supply a large thin flat washer and o-ring in their Steering Box Gasket Sets to go around the sector shaft where it goes through the chassis to stop the flow of grease in that area. Installation entails removing the pitman arm and taking out the steering box to chassis mounting bolts and loosening the upper steering column clamp inside the car so that you can install these parts on the sector housing before it mounts to the chassis. This particular "fix" is far less of a guaranteed "fix" than the End Plate Tube and severe leakage at the sector housing can only be remedied with a rebuild of either the sector housing bushings and a new sector gear and or installation of a sector shaft seal (machine work required) or a rebuilt/new sector housing that has been modified with needle bearings and said seal and the possibility of a new sector shaft to fit the modified unit.
Godd luck, Bob Bader