It would be awesome if anyone knew a good source.
you can try http://www.themelock.com/ecommerce/shopify/
tons of template types, shopify included.
however don’t forget and due diligence before using one for commercial purposes. (check the code, check reviews) and if you end up earning don’t forget to go back to the legitimate seller and purchase the theme in full (you’ll get updates and support the original creator)
I do have a premium shopify theme and I can sell to you at a low price.