Some parts of the Bedford R series and Chevrolet CMP shift mechanisim shar part numbers. I was not able to match the part numbers for the spring shown (assuming it is R series) and the CMP equivalent. To help, the Chev CMP part number is 590388 "Spring, Gearshift ReverseLatch Finger Lever" and it is listed as fitting 8cwt to 60 cwt (including C60X). The same part number also fits commercial Chevrolet 4 speed transmissions 1929-1947 (at least 1947, maybe later - that is the end of my Master Parts book). Do you have the part number from your Bedford listing to confirm if it is the same part?
Google suggests NSN 5340-00-737-7036 may be equivalent.
Apparently the spring was available from GM as late as 1967 (for $0.15)
http://www.antechlabs.com/K0GFM/68Parts/Parts-Gp4.pdf
One online vendor (at least) still lists the spring, but as "inquire for price and availability" so I suspect they are getting harder (or maybe impossible) to find in stock.