The part you are looking for is called a balun. It changes the 75 ohm impedence RG-59 or RG-6 coaxial cable to 300 ohms, which is what older TV sets and most antennas are designed to work with. They are readily available (and cheap) at Radio Shack or any big-box store. They are also available online at a variety of outlets including SolidSignal dot com.
It's also sometimes refered to as a matching transformer. If its just for the back of an old tv/vcr, you don't even need a really high quality one. I've found perfectly servicable ones at dollar stores (99 only on if you have one near you). If you're putting it at the start of the cable, say from a 300 ohm antenna to 75 ohm coax, get a good one. ESPECIALLY if it will be outdoors.