1: - Deep Sea Deposit (Ultima Weapon's Quest)
- Island Closest to Heaven
- Esthar- Grandidi Forest
- G-Garden -Hall (The Garden Crash)
- B-Garden MD System (NORG's Anger)

Cursed Spikes can also be found from Creeps', Death Claws, Forbiddens, Grand Mantis', Imps, or Malboros.

2: You need a whisper. These can be dropped or stolen from Adamantoises, which are found on Long Horn Island and Dollet - Hasberry Plains (both found on shores). Mug the Adamantoises for the item, since their chance to drop them are extremely low.

3: Check here for an extensive devour guide. Devouring is a very good way of increasing your stats later on in the game once you've gained clvl 100.

All info as per is curtoesy of gamefaqs.