Emily,
If you do a search using Google type in "chemotherapy hats"; there are several sites out there. I made a few scrub-type caps for my sister who lost her hair due to cancer, they were easy to make up. I used a couple of the patterns from the sites below.
Not knowing exactly what style you are looking for here's one:
http://www.headhuggers.org/patterns/spatt01.htm
And there are several Free patterns here as well:
http://www.brimmingwithlove.org/
Nancy Zimmerman has a pattern for sale ~ several styles.
http://www.nancysnotions.com/product...rrivals&page=1
Hope this helps and you are able to find what you desire.