Just about all the reproduction parts sellers in the Links section of Stovebolt.com sell Okie bushings (they might not call them the name "Okie").

Here are a few:
Jim Carter
Classic Parts
American Classic Truck Parts

There were three different types between 37-54:
Chevs of the 40s 1937-1939
Chevs of the 40s 1940-1950
Chevs of the 40s 1951-1954