I replaced the gunfighter seat on my '07 Speedmaster with a customized solo. I asked around at custom bike shops to find out who did their seats. I'm sure there is someone in your area. You may want to at least talk to a local customizer to get a sense of what he could do for you. I was able to get a seat with more of a ridge supporting my lower back. It was better, but still got my attention after a few hundred miles. I loved the look of the Speedmaster, but eventually had to give in and trade it for a Tiger. Good luck.
