looks like surface rust on the coupler parts shown. How are the internal parts? Could you disassemble and sandblast?
A few minutes of searching led me to something that looks similar but it's 2". Maybe they don't make 1 7/8 any more.
Here were my searches for reference.
FIRST SEARCH
Drilled down to this product.
These are not your run-of-the-mill trailer accessories. We've taken your everyday products like Trailer Couplers / Ball Mounts and leveled them up.
trailervalet.com
WEST MARINE PICS
Maybe it uses the same spring or other common parts and you could do a combination of refurbishing what you have and adding a few new parts. Maybe call this manufacturer, or keep digging.
UPDATE
Now that I look at your photo it appears that 2" is stamped on your parts and this could be the identical replacement to take parts from.