Tee shirts I get from petsmart, but, what I love are the harnesses that I bought from YT members. Conniedressmydog makes awesome custom fit harnesses, cute and useful! ( way easier to put a Connie harness on than the one I used to use, and I love stuff that has dual uses!
Cinders loves them and everyone in the neighborhood thinks she's adorable when we go for our walk.
A list of members stores are in the yorkie products and review section of the site. You should check it out. Many offer discounts. All are really fun to look at, and most are VERY reasonably priced.
Also, sometimes members will list clothes that they would like to get rid of to make room in the pups closets. I try to keep a watchful eye out for those threads too- same section of YT.