Patsy,
The serial number is on the bed just at the bottom of the pillar.
Go here: {
http://www.ismacs.net/singer_sewing_...-database.html } to date the machine and verify it's model #.
You can find replacement slide plates at Sew-Classic {
http://www.shop.sew-classic.com/ }. They are reproductions but all those I've purchased have fit and worked fine.
Joe