These are the two most likely sources for something like that I can think of, both these guys have reasonable prices and are known, good sellers on this forum.
Don Livingston in MN (507) 433-0073 phone AM best. Jean Claude Marleau L'Orignal, Ontario firstname.lastname@example.org 613-632-9445.
Are you aware that you will need to split the tractor to install a replacement clutch rod.
Personal I would try to restore the existing rod if serviceable on both existing ends. That means that the spring and flat washer are still on the rod in the bell housing and you can pull that end and feel the spring tension and when the release yoke contact the back of the throw out bearing.
The clutch rod is 5/16" dia and ballpark around 17" long not counting the adjusting yoke at the pivot. This is how you adjust the clutch rod length on the 300B series tractors. There is a lot of slop here and you have the adjustment yoke.
The way I would approach this is buy a 1/4" nipple or length of schedule 40 pipe and slide the ends of the rod gap into the pipe leaving plenty of rod inside the pipe clamp the pipe ends down on the rod. With the adjustment yoke centered, adjust the clutch rod per the instruction above. Marking and/or cutting the rod at the pipe ends you now know the length of replacement rod you need to weld in. Personally if the pipe section doesn't cause any interference and it didn't look too red neck I would just weld it in place.
Anyway good luck with it.