Thanks for the info, guys! I've asked the friend who rents our server from GPortal to see if the seed value is visible to her somewhere in the settings, so I can use it in that map that MrBishop077 has provided (thank you for that!)

I kind of thought they never respawned, but my friends kept saying they thought they found some in waters they'd already traveled through that were previously empty. But now I can tell them that that's incorrect.