Yes, but there are other non-magical gnomes that could be in the world. Like the Cat Gnome holding the sign Strays welcome there is two other ones like this for a Dog and Horse. I thought maybe on in Appaloosa Plains they would be out in the world but I haven't found any yet.
You can't steal the gnome in the art museum or the general store .
As far as the gnomes other people have listed. That seems to be all the Magic Gnomes I know about except for Lounge Lizard (lvl 7 singing career) will appear if Fried Peanut Butter Sandwiches are left out. And Cranstan Boonitz will appear if magic is used often gene or witch.
I haven't been able to get the Felix Felinenimus (whacked out cat) gnome to appear or the Carter Caninenimus (best friend dog) gnome to appear. I also haven't had any luck with Sculpting Gnome (lvl 5 sculptor) appearing. That's why I asked if anyone knew of any traits that might help these spawn.
All this and more is what my and JSBrantner's research is for and about.
The non-magical gnomes are basically statues and don't usually just appear but can be seen to be looked at, not bought or stolen, in the general store in France. You can also find them in buy mode under decor/miscellaneous if you own them. There are several of them that come either as free gifts or through store item purchases as part of a set. The holding signs gnomes came with Pets and can be bought in buy mode. There are three of them, cats, dog, and wildlife. Other gnomes that can be bought or are free items are Lucky Gnome, free St. Patrick's Day download, Char-le-Gnome comes with the Viva Las Vegas package, and Holiday Cheer santa gnome came with Tis the Season holiday package.
Sleeping Gnome McMulty is the "generally" found statue/non-magical gnome. He cannot be bought or stolen as far as I know. He can often, randomly, be found via fishing, mining, dumpster diving, (not confirmed), trash rummaging, (not confirmed), exploring the mausoleums, (not confirmed), time travel and exploring mined holes in the ground. He is sometimes found in the mail box instead of cut gems or smelted ore. I have found him most often fishing in lakes or ponds, though I haven't given up on seeing if I get one in oceans or rivers.
Non, magical gnomes never move or strike poses. They are statues. However, the horse gnome, cat gnome and dog gnome, not the ones with the signs which are statues, do move and strike poses. We'll be checking out other interactions. All gnomes that are not statues, move and get into mischief. They all have a variety of poses and actions they do, some more, some less. The most active gnome is Mysterious Mr. Gnome. So far he is the only one who can produce nooboo gnomes and he will age till he dies. Gnome tombstones are statues and can be bought in buydebug. They appear spontaneously when a gnome dies. I have never seen Grim come get a gnome, (yet).
To obtain the animal gnomes you first have to have the animal in your home as a pet. To get the horse gnome you have to have a salt lick on the property and the horse has to lick it several times before the gnome appears. (not confirmed as to how many times, we're testing this one). To get the dog and I believe the cat gnome, the cat has to freak out at the fridge, (not confirmed), and the dog has to bark at the fridge. In a few days they will appear.
For those of you with Seasons, the Ghost of the Darned can be obtained via the Claaaw, I got one second try with normal action and after 34 tries using the fairy cheat action. I believe it is just random. He can also be found on the Fortune Teller's lot and can be moved into your inventory the same as the gnomes in the art gallery in France can. So far I haven't found him anywhere else. We're researching Seasons gnomes now but so far only have information on the witch gnome.
If any of you have any other information please either pm me or JS or post it here. We'll try to give credit for new, confirmed info when we finish writing up the guide article.