Try Wholesale Truck Parts or Anderson Bros. in Portland Oregon.
I don't have a phone number but a call to information should get it easy enough. Last time I was at wholesale truck they had about every model and vintage of Cummins you could want.
Beware alot of the v-6/v-8 cummins had issues with spun cambushings at high hours.
The other option is to repower with a 4BT. ???
Not much help, but I had to post something.
A Johnson