Difficult To Find Ingredients For Herbal Remedies

This guide is pretty good.
Basically the plants that grow in Granite Falls are all marked as unidentified.
You must collect and identify them first - the higher Herbalism level, the better the chance.
Then they'll have correct names in Sim's inventory.

Edit:
If you want a stable supply of ingredients, better plant them in your garden as soon as you identify them.
Insects can only be caught in Granite Falls locations, they spawn like any other harvestable, need to keep an eye out, some are really rare.