try to go to any waterski or wakeboard store.
Follow Murdocs link or type into google your demand. There should some site show up and offer these vests.
I don't know of any but the ones from waterski. Try O'Neill or Neil Pryde.
I wanted to have impact protection in my kite vest. I did quite a bit of looking around the internet to find the best one for kiteboarding. I found it in a U.S. Coast Guard approved flotation device made by Stohlquist. This PFD (personal flotation device)was originally designed for kayakers and such. The design is great for kiting because it does not come down to interfere with the harness. The "shorty" design also bulks up the thickness on front and back sides to about 3 inches each. This thing almost makes you bullet-proof! Plus you have a fully rated flotation device that could save your life if you got knocked silly for a few minutes. I highly recommend this P.F.D. to anyone who is serious about protecting themselves with their gear. It is available at Kiteworld for about 130 dollars. Check it out at: