You could measure the springs, then buy a different rated spring in the same dimensions from companies like Swift. I did this with a set of Megan coilovers, changing out the original springs for a set of Swifts at a different rate (-1K/+1K I think).
Feal, for example, ships theirs with 7k/7k, which will be quite a bit softer than 8K/10K you noted for JICs. That said, using another damper's rate as a reference is not a perfect science. Most of what I've read on the subject suggests staying within 2K of the original rate in either direction, since the dampers were valved to the original rate. That said, it's debatable how much mass manufactured coilovers were really "tuned" to a chassis or valve rate.