Try contacting USGS. They have several 800 numbers and the operators are very friendly and try to call you back if you have a question they can't answer. I have not seen sonar maps free to the public on the web yet.
I primarily work with the free info on the web that has been declassified.

From what I have researched this NOAA map is the best topography data out there now. Someone please correct me and send me a good link if I'm wrong..

Surface of the Earth 2 minute relief map