Need differential locking part for DR field & brush mower

[Tug]

I have a DR field & brush mower purchased in 1998. The cup on the differential housing that allows the locking of both wheels is broken and needs replacing. The differential is good otherwise but the only replacement part available from Dr is an assembly that includes a sprocket/bearings, spacers & many other components I don't need. Is there a source anyone can point me to for a salvaged part at a much lower cost?

Tug

 

[Scrubcadet10]

Will need the model number of the unit.

 

[Tug]

Will need the model number of the unit.

 

[Tug]

Will need the model number of the unit.

"Assembly and operating instructions" that came with machine are for Model ATM125. It has a 12-1/2 HP Tecumseh engine.
I couldn't find a serial # on the machine, but there was an upgrade sent for the operator presence/blade engagement controls that says they are for "Mowers with Serial numbers from 0001 to 5349".