The one you are probably interested in is usually called Vital Wheat Gluten but the really important part is the nutritional information, it's supposed to be 75-80% protein.

Bob's Red Mill is a very well known brand of Vital Wheat Gluten flour.

I've heard of High Gluten Flour but I checked and it has about 12% protein, and is often called Bread Flour or Hard Wheat Flour as well. NOT the one you're thinking of, I'm sure.

Do have a look in the Techniques and Tips section of this Forum, I remember there's lots of posts about commonly used LC Ingredients in there.

Hope this helps.