Yeah, hard to find and not cheap, thats why i'm looking at getting my seat worked on, or possibly buying one of those gel seat pads or something.
I have a 4 hour ride either tonight or in the morning, and its not going to be a comfortable one.
The trouble with any type of seat pad is that it adds to the seat height. The gel seat is more comfortable, but it's not any lower. A Corbin leather saddle is about an inch lower, but I found them harder too. I sold the one I had because it was too hard. But I evidently must be exactly the right height and leg length that I don't experience the nut-cracker effect with the stock seat either so I could do that.
In your case, either get the seat worked on or get a Corbin. The Corbin is lower and doesn't make you slide into the tank.
For your trip....maybe just some cheap foam padding as a temporary measure would help?