It felt odd that the Thieves Guild just handed out some light armor. So I decided to do something about it.

I don't know enough about modding to add these robes anywhere in the game, but you can spawn them by using the console. Search for "Thieves Guild Robes", "Thieves Guild Adept Robes", "Guildmaster Robes" and so on for the other items then add them in. Each piece has the corresponding enchantment to the armor piece normally offered (as in the Robes have Carry Weight like the Armor, etc), and the Adept versions of each correspond to the improved versions of the armor.

This file REQUIRES the latest patch and the Unofficial Skyrim Patch. If you're not using either of those, that's your problem.