I don't know if you want a kit just for ease of choosing fabrics or because you can't find a pattern you like but I've made several christmas tree skirts out of tablecloth patterns. Mine have been square, octagonal, etc. But they usually feature a "center" type pattern that works well for removing for the tree skirt. Maybe not what you're looking for but I thought I'd put it out there.
Good luck in your search.
Oh, and I've ordered from Connecting Threads and they are great.