Kp's in general are kind of rare. There are a LOT of guys here on MCB who horde them because they love them so much. You might have better luck finding a KP3, but they were direct feed and use a hopper not an SC tube. There is usually a few KP2's for sale here but prices usually range from $250-600 depending on condition and accessories. The K2's are more rare and usually fetch $400+ easily unless they are in really bad shape or you get lucky. I would start scouring ebay and craigslist for them, i have seen people get some really good deals there.
You could probably pick up a slightly rough KP3 and have someone like Walz add a SC tube to it and cone out ahead still compared to a KP2. The KP2's are usually more desired and bring more $. Check the ebay sections here on MCB, people usually link deals on ebay and CL in there. You may also be able to pick up a P68SC and convert it to go in a wood stock too. I highly recommend Walz if you want custom wood, he does great work for very reasonable prices.