I'm not sure if certain sweets give certain items or not, but there is some logic to it
With no Halloween staff equipped, you'll receive:
Trick Staff I
Trick Staff II
With no Halloween hat equipped, you'll receive:
Pumpkin Head I
Pumpkin Head II
For the second versions of things, equip a first version of an item and trade sweets:
Wear Trick Staff I, receive Treat Staff I
Wear Trick Staff II, receive Treat Staff II
Wear Pumpkin Head I, receive Horror Head I
Wear Pumpkin Head II, receive Horror Head II
Until you get the first versions of things, just equip something normal in that slot. I traded mostly Cinna-cookies and Ginger cookies to the same NPC and had all 8 of these pretty quickly. I have no clue how to get the pitch fork so far. Good luck. Just keep trading and you'll get them.^^