Staves

[Jacob Saltband]

Are there any magic staves that cast greater dispell magic? I couldn't find any.

[Obolus]

Potentially every magic item you can think of can exist in this game. At the end of the magic item chapter in the CRB there is a chart explaining how to make your own magic items and what their base price would be.

You could easily use this chart to figure out the cost such a staff.

[Thanael]

Rod of negation does greater dispel but only vs. items.

[Atarlost]

The general staff rules parallel the potion, scroll, and wand rules. There's no reason you can't have any staff with any spells you want to put on it. These supersede the general item pricing guidelines and are, in fact, rules rather than guidelines in the same way the potion, scroll, and wand pricing rules are rules.