The Orb of Golden Death
As other answers have noted, the material components of spells in first edition (for which the default setting was Greyhawk), often show sympathetic magic and sometimes contagion. However, it seems the OP is looking for something tied more specifically to the Greyhawk campaign setting itself, and those same 1st edition spells (and their more recent iterations, which often use the same material components) might be used in any campaign world.
One such example of a Greyhawk-specific item is the Orb of Golden Death, as described in the first edition adventure module The Temple of Elemental Evil, itself firmly ensconced in the Greyhawk setting. I will be quoting from the passages in the T1-4 version of this module.
The Orb was created by the demon powers Iuz and Zuggtmoy acting in concert; both of them invested some of their 'essence' in it, although Zuggtmoy contributed the larger share; "things that have been in close contact are magically connected thereafter, particularly if they were formerly part of the same thing."
As with other artifacts of great evil, one needs to beware of close contact with it because of the power of Contagion (ToEE p. 127):
Because of its nature and aura, no paladin1 will touch it willingly, nor will any Good cleric; they feel its immense innate Evil.
This caution is well-founded, for although the Orb grants great powers on any who possess it, the corrupting Contagion is also great (p. 128):
No Good ever results from the employment of the Death Orb's powers, except on a very short-term or temporary basis. Thus, if evil can result from any use of the Orb, that occurs along with whatever was actually done. For example, an elemental conjured [by the power of the Orb] to fight against some evil creatures will do so, but in such a way as to allow them to harm the conjurer's associates to a maximum extent. Also, each time the Awe Power is brought forth, the user actually loses 1 point of Charisma (but only with respect to those not Chaotic Evil)
The Orb, which was created to focus and harness the powers of Elemental Evil (evil earth, air, fire, and water), also shows the power of sympathetic magic, for it is vulnerable to those selfsame forces. In fact, the only method to destroy it is as follows (ibid):
It must then be subjected to the following effects, in quick succession and in the proper order: a wind of 50 or more mph force; the strike of a maul made from a solid piece of granite; a very hot flame (1,000 degrees F); and immersion in very cold water (32 degrees F). The procedure causes the Orb to shatter...
However, the destruction of the Orb also causes harm to the places and powers associated with it, through both sympathetic and contagion magic (ibid):
...which causes the Elemental Nodes and the Greater Temple (Dungeon Level Four, area 417) to collapse, and the dungeon levels above as well. Zuggtmoy takes 111 points of physical damage, is unable to use any powers for four days, and cannot leave her own Abyssal Plane for 40 years. luz, having less invested in the Death Orb, merely loses the services of evil elemental creatures for four years.
1In first edition, paladins are required to be Lawful Good as a class restriction.