Can anyone PLEASE tell me where to find this fish tank ornament?

You can get clay pots at any Garden center. Plastic plants are sold at any pet center or on line at any of the aquarium sites. As for that huge ugly castle I have no idea because I don't think I've ever seen fish in a natural environment swimming around a castle. I'd go for some drift wood with natural small gravel and some natural rock caves and you'll be way ahead of the game.