You will probablt have to get one built.
I would look to the truck folks for a 135 -150A unit that will give great power at high temperatures.
Perhaps $150. Be sure to purchase an alt with OUT a built in regulator (most truck are)
Get a boat 3 or 4 stage regulator from any supplier.
Dual belts on both the drive and alt will lower the maint and increase the belt life.
First place to start is with the engine folks to find out how to add belt groves to the existing engine.
Measure to be sure it will all fit.
Most diesels operate so slowly , and most alts can handle RPM well , that a good gearing up ratio can be chosen.