Hello Datsunrally,
Do you have any friends with a lathe?
I made my own manifold nuts from 1/2" hex brass bar and drilled and tapped for 8mm.
Not sure what thread yours would have been but probably 10mm so would need larger hex bar than I used.
Brass is the best material to use. Do not use stainless as you can get what some call "pickup or galling" when you undo.
If you go with steel just use plenty of never seeze on the thread.