Petfinder. Like match.com for pets. We got our last 2 shih tzus (Buddy & Chip) from their rescue places. They have many (from 3mo old pups....to seniors) dogs including Shih Tzus avail all the time. You can search the site by breed, location, age, etc etc.
Strongly recommend that you adopt too. Here's a link>
https://www.petfinder.com/pet-search...baby&age=young