This?
http://www.clamptitetools.com/shop.html

I would not buy a special tool just for tightening wire.
Most people I know just use a pair of pliers.
It is an expensive little bit of kit too. I bet if you look at it for a minute or two you can figure out how to make one out of a bolt and a piece of scrap tubing fairly easily.

You can find those in stores that sell woodworking and gardening tools if you really want to buy one.

Maybe you are thinking about the twister tool for closing sacks, but I don't think you are.
http://www.rhodespackaging.co.uk/acatalog/wire-sack-ties.html
It takes premade twist ties and you yank on it to twist the ties shut around the mouth of a bag. You sometimes see them used on potato sacks.
It is a pretty specialized item.