It's not always as simple as getting a longer stroke shock I'm afraid.

Some frames (e.g. the old Specialized stumpjumper and Giant Reign) let you do this but other's don't have the frame clearance.

 I reckon your best bet would be to go ask about on one of the dedicated Kona forums on mtbr.com.  You're likely to find someone who's looked into it.

Also bear in mind that by increasing the length of the shock you could be raising the bottom bracket height and affecting other angles etc.. not necessarily for the better!