I find Etsy to be great for stuff like this.
Middlesbrough mug - Etsy UK
Check out our middlesbrough mug selection for the very best in unique or custom, handmade pieces from our shops.www.etsy.com
There is also Red Bubble too:
Middlesbrough Fc Coffee Mugs for Sale | Redbubble
High quality Middlesbrough Fc inspired Coffee Mugs by independent artists and designers from around the world. All orders are custom made and most ship worldwide within 24 hours.www.redbubble.com