Cannon racecraft I believe can make about any spring you need. I used them for springs on another bike and dealing with them was a great experience. If they don't have the spring you need listed give them a call and they can probably make what you need. http://www.cannonracecraft.com/
I just installed a seat concepts last winter and maybe it's a little bit more comfortable but it's a little taller than the stock seat. Overall I kind of wish I had kept the stock seat. I looked at Seat Concepts site and they no longer list a low option. Just for reference I'm 5'9" and 240. I...