If your rates and quality of termination are competitive, finding companies to send you traffic is fairly easy. Posting your rates and payment details on the following websites should get you some response.
Another surefire method of obtaining traffic is to become a member of Arbinet (www.arbinet.com), which is an exchange of long distance providers and companies that are originating calls. Arbinet essentially handles the task of finding companies to send you traffic. Presently, the Arbinet membership fee is approximately $15,000.