Buying Football Kit(s)

Hello, I am visiting your city next week and when I travel I like to purchase the local football team kit.

So I was wondering if you could recommend any stores that would most likely have kits in stock? It doesn't have to be from this season, but it does have to be an authentic kit.

I would prefer to not have to go to the stadium to purchase the kit if possible, but if it is the best option then I will do that.

Thanks in advance for any replies.