If you are just starting out it might be fine to use these directories but you would be best off cultivating a local reputation in the first instance. You can let attorneys you have worked with know that you are always available, and offer to give talks to the local bar association/trial attorneys/district attorneys/public defenders etc to get your name out. Your reports are your best form of advertising too. I would cultivate a relationship with attorneys you have worked for in the past to let them know that you are available and they should feel free to give your name to anyone looking for a psychiatric expert. I'm just starting out my forensic practice myself 🙂
I noticed you said you don't ask for retainers!!! Always get a retainer (and then when it runs out, a replenishment), you will get stiffed eventually (I have been). Never do any work without getting the money up front. Also the retainer should be non-refundable. If the case ends up not getting anywhere, then you still keep the retainer. The exception is government agencies who should always pay (though that has not been my experience) and won't usually give a retainer but you can certainly still ask. Plaintiff's attorneys (aka ambulance chasers) can be particularly sketch.