Not sure if you're crafty at all, but you can always attempt making one!!!
http://sewing.about.com/od/freeprojects/ht/treeskirt.htm
OR
and I swear, I am in love with this site and probably spend hours on it a week.
Etsy
It's a site where people can sell handmade items of any kind (side note: they have a great pets section, which i'm a part of, but won't link here cuz i don't want to advertise selling or whatnot) There's THOUSANDS of people on there.
Anyways, my point is, they have a section where you can request for things to be made and the members bid on who gets to make it. You can list a price for it as well, so they know how much you're willing to pay. It's probably your best bet if you want something done well and you get creative custom control over it.
Here's a link to that specific section in case you want to go that route:
http://www.etsy.com/alchemy/