Check out the OLDIHC forum, oldihc.org I have a 1951 International pick up and spend quite a bit of time over there and have often seen numerous GRD motors or motor and transmission combos for sale as the civilian K's and KB's used them. They have a classified forum on the site but also look at the forum called "Diamonds in the rough" Member post links to ebay listings plus listngs from craigs list from all over the country for IHC trucks and parts. Green Diamond "flatties show up on that sub forum as well.
They have a military vehicle forum there also although it doesn't get many hits. After missing out on an IH military I ended up with my current Chevy Truck............wish I could have both!
Jerry Biro, Hercano Propulsion, did have an NOS Green Diamond 233 a few years ago. This is a late 30's thru 40's engine.
PROUD 2011 MVPA PIONEER AWARDEE-HONOR GRAD WHEELED VEHICLE MECHANIC SCHOOL 1960- US ARMY ORDNANCE SCHOOL(MACHINIST) APG 1962 - O-1 BIRD DOG CREWCHIEF - 68 NONSTOP BY THE BOOK ARMY TRUCK-JEEP YEARS LIFETIME AM LEGION DAV 40/8- MVPA 1064 -7 TURNKEY MV'S