Try ebay or American Society of Dowsers, or do a Google search for dowsing rods. As for witness, if you use one rod you can hold a witness in your opposite hand in your fingertips. I've heard between your thumb and index finger, but since your fingers are alternating polarity, maybe the thumb and middle finger, I don't know. Another way is to press the witness against your forehead (the lower part). I've heard that metal witness like gold can affect the rod if it touches it, I don't know, don't use one.
Some people even write the word down on a piece of paper and use that for a witness. The idea is to impress your subconscious, and the best way to do that is when you use emotion. Positive or negative both have a big effect. If you use negative (doubt, fear, etc,) of course you will destroy your dowsing. I read a yogi (Rumi Da) says he likes to think of his puppy licking his face. Try to achieve a joyful state of mind, or wait until another time.