Hi, You can find developers on freelancing websites like Odesk, fiverr, freelancer, peopleperhour etc. These sites allow you to post your requirement and then the candidates bid for your project with their quotation. You can pick one based on their skills, experience and your budget. You can even look for a web design/development company to develop your project. These companies have a team of skilled professionals that can develop your website.
You can even look for a responsive theme on Themeforest. I recommend to purchase a genuine and original theme developed by a professional. Sometime there are vulnerabilities in theme that could cause issue .