I buy them in bulk from Home Depot, or Target. But I use them for all types of things at work and around the home. I found a box of 50 mixed size black cable ties in the electrical section of Home Depot for 5 or 6 bucks.
I was this (fingers almost touching) close to getting the Cateye wireless, it looks like a great device. I ended up going with the Planet Bike 9.0 wired since the range is not long enough to work on an indoor trainer. Also for training we picked up a Mainnav 600a (http://www.mainnav.com/product/mg-600a.html) for Google Mapping.