If you have a good eye for patterns and know how to alter them, you can make enough changes to commercial patterns to make them unique. Many commercial patterns are easy to alter - once that's done you have a unique pattern and no-one can accuse you of theft or misuse. If you take a look at several patterns (for dolls or humans), you will see that they are all based on a few basic shapes which are then made into different pieces of clothing by adding darts, different sleeves, different lengths, etc.
Also, some of the people who provide free patterns on the Internet may be willing to allow you to use their patterns if you simply ask for their permission. It might mean you paying them a small user's fee or royalties, or they might even allow you to use the patterns for free.

RP.....I agree with the above poster..look at the patterns available...most of them are nothing but circles and rectangles of fabric..some of the bodice patterns are even hardly more than that and no matter which pattern company you try..they are all basically the same....after you have made a few from a basic pattern you can make your own.....

I have seen Mattel brand barbie patterns for sale in fashion pattern books at fabrics stores, but that was some years ago. I would contact Mattel and ask them, or try looking in fabric store books.

Go to a fabric store and read on the pattern. If they are copyrighted it should say on the pattern or call the pattern company. I see Barbie clothes for sale at doll shows all the time.

If it has a copyright leave it alone it's not for commercial use.

I'm glad you are trying to do this legally.

Usually that would mean making up your own patterns or working with a designer and paying them a royalty.

Thank you for being ethical in your business dealings.