If it's the manual for a Sears Electric 120-49 Kenmore Sewing Machine you're looking for, try homeappliance.manualsonline.com. There are other online sites provide Sears sewing machine manuals, as well as advice and spare parts though...
For example, the site sewusa.com provides manuals for the whole Kenmore range, although they do charge a fee for the service. The site also provides a few tips for sewing with the Sears Kenmore models.
Artisanssquare.com has a forum thread devoted to the Sears 120-49 Kenmore, with a lot of postings from people who own and use this model. If you have a question of your own, why not join up and join in the conversation?
The online Sears shopping site shopyourway.com has a 'library' of Kenmore manuals, not just sewing machines, but every product made under that label.
Aside from checking the usual auction sites such as eBay, you could try Kenmore themselves by phoning 1-800-549-4505 or 1-888-536-6673, or email them via the Sears website.
You might not expect YouTube to be much help when it comes to sewing machines, but there are films demonstrating how to use Kenmore models, such as this one: