The world specific items aren't (tree of prosperity and wishing well) but I did see the grill for sale in game while it was still not sold on the website. I didn't buy it, so I'm not sure if it would have worked but I would go into the game and into a household and into buy and check it out. If you click the gold coin it will offer more store items. GL!
I'm pretty sure none of those are available separately, you'd have to buy the world or venue they come with. Sometimes objects (the Teppanyaki grill for instance) are listed on this website as not being available for purchase separately but can actually be bought separately on the store when you're playing the game. Probably a glitch. But I can say for certain that the 2 gambling ones can't be gotten separately because I am interested in getting those as well and specifically had a look on the store while playing the game to see if they showed up but I couldn't find them.