What your seeing is not a brass rod it is a cup style seal in a brass base. They work alot like the seals in an automatic transmission and seal tighter the more pressure they feel. You can find these at www.mikesubworks.com
Another option is offered by www.caswellplating.com They offer an oring style seal that is encapsulated in alumilite.
Also you could use an aircraft serco boot and just silicone it in. These are great if you need some slop in your throw and they are very cheap. You can et these at mikes subworks aswell.
Lastly you can try the same style the Dumas Akula comes with. It is simply a silicone hose glued to the bulk head and a tight fitting brass rod going through it. I dont recomend this for deeper dives.

Any more questions?