The Letter People are still available in their new format if you wish to buy them. Abrams Learning Trends has a complete program and various features for parents and teachers. For those looking to the older sets, auction sites are likely your best option. However there are some sites that can help with pictures, lyrics, and other Letter People information. You can find some of those links here. Read more...
Abrams Learning Trends
Bobopolis Letter People
Lyrics to the Letter People Songs
Pictures of the Original Letter People
Resources of the Original Sheets from Smokey Mountain Homeschool
I'd suggest researching this one. I couldn't find anyone who had experience using it.
Teacher CD Resource of Original Letter People
Image copywrited by owner not for reuse