Introduction: DIY 300 to 75 Ohm TV Antenna Coaxial Baluns
Here are 2 sites I found with information on how to make Television Baluns.
However, depending on your situation though, You might just go to the Deseret Industries and pick a professionally made Balun for 50¢.
Step 1: Find Parts and Start DIYing
The websites I have found so far are below.
This site has the most information and schematics
Have fun DoInstructibleYourselfing.