D2 3J Water Pump Overhall

Ask at any industrial supply company or pump service shop. The square "rope" packing is commonly used in industrial pumps. There are various sizes (the "square" dimension) and differing lubricating compounds available. Graphite is common, also teflon, possibly others are available.

Take note that the lubricant that ultimately keeps the packing from getting hot is coolant. The packing should be tightened so that it does not leak "too much"😆 It's hard to keep one totally dry when you stop the engine and also have it stay cool while running. Probably will have to put up with a little seepage with it stopped or it will get hot while running. If it gets hot, it will wear the packing quite rapidly compared to if you keep it adjusted properly.

Adjust it slowly with the engine running, you want to let it drip some initially and only tighten the gland nut enough to stop excessive leakage. If you tigten it when you stop the engine, then plan on loosening it again when running, possibly while the pony motor warms the main engine up.

Try mcmaster.com

If you are not near a large town or city plus find it hard to order small orders. I would recommend junk yards for large gate valvles where they would let you remove the packing from the stem as they are probably scrapping anyways.
Or a farm tractor supply, automotive type of shop or a boat yard.
Just throwing you some options!