KP parts can be found here:
If you are upgrading an original KP you will need the a Valve, a KP Cup Seal and a Regulator. This will essentially give you a KPII and reduce the farting significantly. It won't completely eliminate it though. You can try using spyder spring kits in the KP to reduce/eliminate the fart sound. Unfortunately I don't have any recommendations for what spring kit to use.
NOTE: The KP cup seal can not be found on the online store. You will need to contact the US office to purchase one. You can also purchase parts from the US office as well by contacting us at 909-468-3600 or via email at firstname.lastname@example.org