Is there a guide on what is available and how to unlock them?

Not really.

There are 3 Autumn - Not 100% sure, but I think its give 1000 items to the bonfire. Luminaire - free 1000 fairies Morostide - carve 500 pumpkins

I think both the luminaire and morostide ones can be done any time of the year. The autumn one, if I'm right, is only available during fireside since it requires tossing items in the bonfire.

Hey , thank you for responding! (sorry it's taken so long for me to come back to it, I think it got buried under other notifications) I've gotten the Morostide and Autumn ones, but I have a long way to go for the Luminaire one in that case.

no problem :)

Its a very good time to buy the snow fairies, even if you don't have time to release them. A big bunch are going from 800-1500 sP.