This is one you can make yourself, cheaply and easily:
Take a long bolt and two nuts (1/2" head, as I recall).
Thread one nut onto the bolt leaving a couple of the bolt's threads visible.
Then thread the other nut on so that it is half on-half off.
Tighten the "inner" nut against the "outer" one so that neither will turn.
The half-off nut can then be screwed onto the grease cup's threaded extension, and the long bolt should protrude sufficiently for the whole thing to be pulled easily out.
If it sticks, try warming the hub sides with a torch to loosen hardened grease.
If needed the bolt head can be grasped and pulled more firmly. I think I could even use a slide hammer on it, if I had to. But remember, you've only a few threads' grip on the cup
Using pliers on the threads will damage them and make this approach harder.