You can see a market place to sell these when you enter the Terra Cotta Warriors. Also, youc an find in the souvenir shops in Suyuanmen inside the city wall.

I Think ShuYuanMen are good place to get the goods you want,since they have all feature local souvenirs.However,as the terracotta warriors things are all big guys,you can consider going to some local plant where they have their own exthibition,now they supply many products to foreign country,give so much help about broken, fade,change color after you receive your favorite soldiers.Some old and experienced plant can promise you resend new one if you received broken ones.
These some suggestions i can provide.you can know something about the qulity and after-sales service from their website.
I hope you can get your satisfied soldiers,any question pls feel free to contact with me.Thank you