Red spiner eggs in Arandar. You'll need to dig at the location shown in the map below while having the clue scroll and navigation tools in your inventory. Be ready to fight a powerful lvl 108 wizard, you'll need to use the protect from magic prayer, the wizard will still use a dragon dagger to attack and will most likely poison you.

Required items: clue scroll, watch, sextant, chart, spade, anti poison, melee armour, weapon, teleport runes and food

Required quests: Regicide.

Possible way of transport: Walk from Ardougne and go through the big gate which is north of Arandar.