Additional thoughts for the original poster, as he may not be aware.
Any lock that is part of your mastering system will contain the secret masterkey inside. All it would take is a renter with a curious son who removes one of the locks and peers inside. With knowledge obtained from the pinning configuration, he could then obtain a KW1 blank and make his own master key, or ask the hardware shop to make one for him.
If you are looking for Kwikset pinning kits, you will find the best deals on eBay. I would recommend the following auctions. If the auctions have expired by the time you're ready to buy, simply look at the seller's current auctions and you'll find the same set.
$24.95 + $5.00 -- Locksmith, Handyman, Pinning Kit for Kwikset (NEW)
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 6049112726
$24.95 + $4.95 -- (NEW) Locksmith Kwikset Master Pinning, Re-keying kit
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 7603810578
There are certainly other kits on eBay, just pay attention to what you're getting with the kit. The two above kits are very similar, except the second comes with master system pins. I suspect you'll get more of the 1-6 bottom pins and more misc parts in the first kit, but you'll need to contact both sellers for detailed specific counts.
Good luck.