Unfortunately your kinda boned. Best I can say for you is get on a boat and head toward the ice cave facing south .. east of swamp so your safe there..go in with the intention of gathering a lot so you don't have to make another trip for a long Time. If you only need like 10-15 you can boat over to the island east of your islands [has a wall on it and steps leading up] there is a hidden secret cave under it with I believe 5 crystal spawns.