Here's a few that Dog. com has available:
Dog Supplies, Dog Beds, Toys & Treats Supplies Search - Dog.com
Here's what Petco has to offer:
Pet Food, Supplies & Accessories at PETCO
Or if you are crafty and have a hardware store nearby, you can make your own like I did.
GEDC0919_1.JPG It's just a simple pvc pipe frame covered in chicken wire.