The parts are in there or the shift handle wouldn't stay on the shaft. Disconnect the shift lever assembly from the connector, and remove it from the vehicle. Press in the two pins and it should come apart. Probably the spring is broken or the bushing is worn out. Those are the correct parts to fix it.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine