Soft seat springs

[YoDA]

I'm helping my bro. with his bobber and one thing I need to change is his saddle springs. The bike has a Pancho rigid frame and the spring under his seat are so stiff any time he hits a little bump in the road it about knocks his teeth out! So I figure a set of softer springs would do the trick. Anyone know a good source for a set of soft springs or another set-up that might work?