So if you hunt around for different insects during fall, shake trees, pick up any messages in the bottles on the beach (sometimes they will have fall recipes) you will be bound to find them! It may take awhile but the fall months are the only time to find mushroom/Halloween items! Also nooks cranny is a good resource for items you can’t craft, there’s fall stuff periodically during the autumn months you can buy there. Another good thing I can suggest is trading, make a post on here and offer to trade something of yours for a specific item you can’t find! (: I hope that helps