Check on ebay to see if anyone is selling the pattern leaflets. I don't remember if they ever published the patterns separately or they were only with the sweater kits. They were popular from the 70s into the early 80s. I remember there was Big Bird, Burt and Ernie and Cookie Monster and Oscar for sure. There were tons of knockoff patterns for Miss Piggy and Kermit too. Back then the patent police and copyright attorneys were less active, and it was very common to see ads for patterns for Priscilla Pig and Ferdie the Frog, but they were clearly designed to be muppets.
"antique" dealers in the south and midwest often have stuff from this era when they clean out senior's houses.
If all else fails, get a couple of coloring books that have Sesame street characters and trace them onto knitter's graph paper. It's not really difficult and the drawings are simple enough to translate well.