The throw out bearing has a tiny hole for grease. And have to go thru a small access hole to get to the bearing. What grease gun or applicator would it take to get in that small hole?
There should be a grease fitting in the hole. Is yours missing or are you talking about the hole in the fitting? Chances are you have a replacement bearing fitted and are only greasing between the bearing carrier and transmission input shaft. If you have modern style fittings on the rest of the car and original style in this location you will need to buy or barrow an adapter to grease it. The parts suppliers carry them.
I wonder if someone has ever tried to drill a tiny hole on the throwout bearing and inject the bearing with grease and then seal the hole if some kind of epoxy/sealant. I guess you would use a needle and then fill as much it will take, and then run the bearing a minute to recirculate the injected grease & repeat this to get it all around the bearing.........
If your bearing has provisions to be lubed it will get the grease via the zirk fitting on the throughout collar. I have one like that. most newer throwout bearings come pre lubed and have no way to grease than by hand.