Go to your fabric store and look at the pattern books - they're usually in the back of the books - I forget what they are listed under - perhaps as crafts. Bad memory!
Also, be sure to do a search on YT. There are some things on here.
And, finally, go to GOOGLE and put in "Yorkie Clothes Patterns" and also try different terms, such as "doggie clothes patterns", etc...
I wish you luck. I used to make some things many eons ago - before they had patterns for doggies. I hope someday to do it again.
Have fun, too!