Is Rishworth the only contractor for them?
No, Parc Aviation and Rishworth share the recuiting efforts. But, if you have already had Rishworth (or Parc) begin any recruitment process on your behalf, you will not be able to change agencies. There is an accepted rule that once one agency has you, you cant' change to another UNTIL the end of the first contract. Even then, changing agencies is subject to all sorts of different criteria and approvals.