RIFT’s 1.9 update will remove the option to spend certain world event currencies, so spend them if you’ve got them. With update 1.9, rewards associated with Otherworldly Sourcestones, Ancient Golden Dragon Egg Shells and Rune King’s Seals will be removed from the world event merchants. This is part of a planned phase-out of past world event items, which will continue in phases beginning with 1.9.

In addition, RIFT's update 1.10 will also see the removal of rewards associated with Dragon Tears and Magma Opals from vendors, however, rewards associated with Unique Snowflakes, Glass Beads, and Carnival Prize Tickets will remain available and the currencies will be updated.

Source: RIFT 1.9 World Event Merchant Changes