The Star Wars Holiday Special aired on November 17, 1978. Along with new live footage, the program featured a cartoon produced by Toronto-based Nelvana Studios that officially introduced Boba Fett.
Unfortunately the Star Wars Holiday Special was only aired once and has never been officially released so the only existing copies are of exceedingly poor quality.
Note that Boba Fett carries two weapons in the Star Wars Holiday Special that aren't seen again. The first is a Sacros K-11 pistol, also known as "The Disintegrator" which is very similar to the Concussion Grenade Launcher Boba is seen wearing on his hip in the Empire Strikes Back. The second is a Amban phase-pulse blaster which has a distinctive two-pronged barrel.