There are many web sites devoted to listing free manuals of vintage sewing machines. Many of the following links are from the long hours of John Langdon, member of ISMACS and long time sewing machine collector. When you find a link to your machine, send him a silent 'thank you' and share the links with others.
As the web is ever changing, you may find a "dead" link. Send an email to charlene@thesewbox.com if you run into one.
There are many wonderful groups to join and I certainly recommend ISMACS for wonderful articles, photos, and research of our lovely vintage machines.
ISMACS has just added a manual page for around 2,000 links - many machine models