eBay is probably your best bet, I am a pretty big jersey collector. There is a website called basketballjerseyworld.com based out of Australia that has a few college jerseys, but mostly deals with NBA jerseys. There are also a few people who sell off of their Instagram accounts, specifically rare_wear_attire, but again they deal mostly with NBA jerseys.
If eBay isn't working for you, I suggest checking out projerseytalk.com. They have a subforum for everything, including NCAA, items for sale, and item requests, so you can always register there and see if anyone has anything for sale.