I just got two new ones today for my '48 1 1/2 ton from Carquest. They actually had them in stock. I think it's the same rearend they used for many years. What you may have to do is take your old one out and find the part number on it and see if a parts guy can cross reference it to a modern number or measure it up and find a match to it.
Good luck,
Scott

Scott Ward

2 1948 1.5-ton Loadmasters
The red one and The snow pusher
1 1950 3100
1 1955.1 Chevy 6500
1 1954 Chevy 6500 2-Ton
1 1955 1st Series COE 5700
1 1963 K20 (454)
1 1964 C10 (350)
1 1951 1.5-ton Dump Truck
1953 and a 1956 Ford F800

Raising a teenager is like trying to nail Jello to a tree!