Where Can I Get Garlic Wreaths?

Use the cheat bb.showhiddenobjects and then search for garlic in buy mode.

If you don't want to use cheats you could also download a room from the gallery with garlic items in it.

There are other ways of obtaining garlic besides growing them.
1. Ironically, the vampire world Forgotten Hollow has garlic plants located near everywhere. You can find some behind the large uninhabited house. In the new game, the garlic plants may not have grown by then, so multiple visits are required.
2. By clicking on the computer and choosing Order... you can order garlic seeds. Actually, one garlic seed pack has 2 garlic (not seeds) ready to be used not only in planting, but also in cooking or making the garlic wreaths. No vampire lore skill needed! But it can get expensive.

But other than making the garlic wreaths (which requires vampire lore skill and garlic), you can buy these in buy mode if you enter this cheat:

bb.showhiddenobjects

Search garlic and you'll find it. Other ways are getting a room from the gallery that has the garlic wreaths. The only annoyance is that you'll have to repaint the wall and floor to make the room normal again.

You can grow plants in an apartment. But as someone else mentioned you can also order it on the computer. Since you're in the city you can also try the produce vendor that shows up there.

You need the Vampire Lore skill to actually learn the recipes to be able to make them. I think it's Level 5.