I do not have one
Perhaps you should edit the title of your post to replace "for sale" with "wanted". The thread title makes it look like you are selling one, not looking to buy.
car-part.com doesn't seem to have a category for those, so perhaps its a thing that junkyards don't inventory. Might be worth a call to a local junkyard to see if they might have one though
I didn't like it when car makers started providing donuts instead of full size spares. I've heard a lot of new cars don't even come with donuts, just a can of tire inflator. I like that even less
The vehicle I had before the Vibe had a donut, and I had to use it once. When I let the jack down, I found out the donut had lost pressure, I had never checked it, and the tire bead broke free from the rim. Not the kind of thing you can reseat on the side of the road. lesson was to periodically check the donut tire pressure.