The key benefit of Bootstrap is that developers can get a nice looking design off the ground without spending a large amount of money on a designer.
That said, the problem with the barebones bootstrap now is that there are far too many sites on the web using it -- and thus all look the same. It's fine in the MVP (minimum viable product) stage, but later on you should strive to create a more unique design language for your app.
If you're still in your MVP stage, I would recommend:
1. Buying a theme from ThemeForest (they're some really great bootstrap themes that'll barely cost you $40).
2. Use one of the following tweaked Bootstrap templates freely available:
Once you are out of your MVP stage (validated the idea), you can indeed find awesome designers on Dribbble. You'd want to pay for their Pro version which gives you access to search for designers based on criteria.