A crystal teleport seed is a teleport crystal that has run out of charges. As with all crystal equipment, a crystal teleport seed can be recharged by Eluned. The charge fee starts at 750 coins and decreases each time a crystal teleport seed is charged, until after five chargings a minimum price of 150 coins is reached. While completing Song of the Elves, a teleport crystal cannot be recharged from Eluned. Instead players must speak with an Elven Scout where Eluned can normally be found. When Song of the Elves has been completed, players may recharge teleport crystals from Eluned in Prifddinas. Players may possess multiple crystal teleport seeds at any time.
For an exhaustive list of all known sources for this item, see here