So I recently started a chaotic good dunmer stealth mage, who has a cover identity. She acts as a woodsman, lives the dull life of Riverwood at day, and kills bandits, and tries to track down the Dark Brotherhood at night.
There is an issue though. I'm going to reach 50 in my magical skills (illusion, conjuration, and destruction) soon, but there are no spell vendors other than the College of Winterhold at this level.

So basically what I can do is

1.Join the College and ruin my roleplay
2. Not get better spells and be unable to cast illusion spells on higher level enemies.

Or is there a third option? Could I circumvent joining the College somehow?
Please post your ideas.

BTW I'm playing on the 360, so no mods possible.

Just "tell" everyone that you have a sick/injured relative up north that you're going to visit to help them out. Zip off to the college, buy the spells you want, head back home