Hey,
I wanted to buy some conjuration spells in Chorrol's mage guild, but no one seems to have the button to buy the spells. Suggestions?

Try again later. Usually, when you can't buy items/spells from an NPC who normally sells them, it's because he only sells them during a specific time of day.

Why is this in the mods section?

forli is right; oftentimes those mages are on an extended cigarette break it seems. Even in the vanilla game. Sometimes they'll be standing right in front of you, you know they have the ability to sell some spells (or recharge weapons) yet they're not offering their services at the moment. You wait and you wait, and sometimes they'll finally they're back from their 'break', but half the time they're not. It can get to be frustrating.

One thing that might help is to go have a look at http://www.uesp.net , dedalus. Go in the Oblivion section and search up Chorrol. Follow the links to the Mage's Guild, then follow some links to the particular NPC you want to buy things from. UESP is good at explaining the schedules various NPCs are on, assuming your problem is not mod-related.

HTH