Simplicity patterns has some. You can look at

www.simplicity.com

Sue

Try local thrift shops, also if you have a local pet store, they usually have a bulletin board where you can post a "wanted" note, or even check to see if your local animal hospital has a bulletin board. Then there's Freecycle. Some vendors on eBay will accept money orders. HTH

Here's a free one. Cute!

Here is a link that might be useful: Dog Dress with Pattern