Here are some links you may find interesting:
A website dedicated to other Yamaha Superaxes: http://www.alston-family.co.uk/
A website dedicated to many Yamaha instruments, including guitars: https://yamahamusicians.com/forum
A website dedicated to other vintage Yamaha guitars: http://www.yamahaguitars.nl
NO LONGER ACTIVE A website dedicated to Yamaha Super Flighter guitars: http://yamahasuperflighters.co.uk
A website dedicated to the early Yamaha SG guitars: https://screamingyamahas.wordpress.com/
You can download the “Yamaha Guitars And Guitar Amplifiers 1968” brochure from this link (Preservation Sound): http://www.preservationsound.com/?p=1495
Here some youtube links for SA30 SuperAxes: