do any NPCs sell cheese wedges?

[Kojak]

or anything less than a full wheel of cheese?

 

[Dot_Warner]

No. Wedges are a begging "reward."

There is a wheel of cheese with a wedge taken out of it, which I believe comes from the Create Food spell.

Edit: Yes, the wheel of cheese with a wedge taken out of it can be created using the spell.

 

[Acid Rain]

They also drop as corpse loot on lesser spawn. Cavern of Discarded will drop a lot.