In my adventures through old antique shops I found this little gem. A BSOA merit badge series on Electronics. Inside includes a very simple monophonic toy organ schematic with instructions.
DIY Toy Electronic Organ
You can have a lot of fun building and playing this small electronic organ, which is made on the same principle as the large home or church types. Although it only has eight keys, it has a switch to throw it into bass range for deeper notes.
Click images for full size. I'm going to try building this once I get some more free time, but wanted to share for anyone else interested in making a DIY Toy Organ for fun.