When referring to stern drive power packages, 'bell housing' is the part attached to the gimbal ring that the drive bolts up to. I think you are referring to the 'flywheel housing' on the back of the engine. And as such that spacer is part of the rear engine mount attaching hardware. And it's not available separately, you need to buy a full 'bolt kit', as Bondo had said...
If someone walked into my shop and asked for a couple, I would grab up a piece of thick walled alum tuning with a 1/2 inch hole and toss in a saw. 5 minutes max. Surely there is a small welding business nearby.