I wish I could offer... not in my wheelhouse...
But if you have a schematic with parts listed, what you need is someone in the electronics field, not in the "pre-amp" world.
Someone outside of this industry.... follow the directions, etc.
In terms of "discontinued parts", you need to look at one of recent pre-amps, where the parts are not old. I would be
willing to bet since they only build something like 100 basses per year (just a wild donkey guess) that they can not commission
proprietary components. They are not Fender... Someone is supplying their parts off of the shelf.
So many falsities on the internet that reverse engineering would eliminate...