Verified answer

the glass armor doesn't appear in the game until you're about level 20-22. there is no specific place you can go to get it before. once you are at the right level, it will be in the stores and everywhere else that you find armor and weapons (ie dead bodies you've killed).

below is the link for all armor and weapons:

There isn't a single place where everyone has glass armor. Glass armor will appear on bandits and in chests randomly after you hit level 20.

However, if you buy the Orrery expansion from Xbox Live, the bandits that you have to deal with in that quest will most likely have a good set of Glass armor for you.