Can anyone tell me where I can find something that has either a fortify destruction or fortify conjuration enchantment on it? I'm trying to get my hands on one so I can disenchant it, but so far I can't find anything. The fortify magic + magic regeneration ones are easy to find on robes, but those enchantments only work on chest items. I have about 3k gold, so even if i have to buy it, that'd be fine.

Thanks for any help!

It's just random loot and randomly stocked at shops.
Thalmor robes have fortify destruction.

The College of Winterhold has vendors that stock them.

Where do you find Thalmor? I've yet to encounter any Thalmor in my game. Do I need to get to a certain point in main quest?

that clothing store in solitude has the largest selection of enchanted clothing.. you could try there.