When you follow your sim around whatever world she is in at the moment, keep an eye out for magic gnomes. They will appear in random locations around the world, but there are a few objects in the world that will attract them more than others.
In Champs Les Sims, you may find magic gnomes hanging out at the museum. Sometimes they are on pedestals and displays, like this Little Léon gnome, other times they may be found admiring relic displays or just out in the museum gardens. Also, it’s not just this gnome that you will find at the museum. The museum has displays for all of the adventure worlds, and you will find all three adventure gnomes there at various times; in one of my recent games, I found a Little Léon, a Sultan Sam and a Master Manchu all in the same room at the same time on separate pedestals.
The invention and sculpting gnomes are attracted to the inventor’s workbench and sculptor’s studio respectively. You also might find a Lounge Lizard singer gnome or Cranstan Boonitz magician gnome on lots where singers or magicians live. When there are a few snowmen on a lot, keep an eye out for the s-GNOME-man Bittertotter, and when your sim is scuba diving, Mr. Mariner will sometimes appear at shell spawner locations.
In general, if you see a magic gnome in the wild, you will usually be able to click and drag it to your sim’s inventory. Once it’s there, click on the gnome and give it a name; that will ensure that the gnome stays on your lot when you place him on the ground.