I get a lot of my stuff from TJ Maxx, Marshal's and HomeGoods which are all owned by the same company so if one store does not have a size the other two might.
I do a lot of ordering from, they have great sales and ship super fast!!
Dog Clothes in the BaxterBoo Dog Clothes Shop
And this is another site I use...
Dog Clothes | Dog Clothing & Puppy Clothing - Dog.com