It is so easy to get locked out of almost anything, I always try to keep a second set of keys. You can always call a locksmith or check where you purchased the carrier. Maybe the expert has a better answer. Good luck.
I know with Thule racks you can call them with the serial number off of the tumbler (the thing the key goes into) and they will send you another set of keys for a reasonable price. You might want to contact Kar-Rite and see if they have a similar service.
I still have my original manual that came with my Karrite carrier and they have the info right in the manual. You can call the company at 800-KARRITE give them the code on the lock and they will replace the keys for a fee of $5.