A recruitment agency will generally maintain a database of interested candidates and in professions where it is likely that this is the only source of candidates then we recommend that you continue to work with a specialist recruitment agency. Also, in very senior posts, specialist headhunting agencies will be the most effective tool for sourcing good quality candidates.
However, for many jobs, the most likely source of candidates will still be professional journals whether accessed by the candidates via the journals themselves or internet websites. For example, if an accountant or HR practitioner is seriously looking for a post they will always read their professional journal careers pages as well as possibly registering with specialist recruitment agencies.
You do not need to use the services of a recruitment agency to access these candidates!