There are lots of places to get one. It all depends on how much you want to pay. Prices will vary from seller to seller. I saw one on CL a month ago for $45 but it had no cord/pedal. Carefully read the descriptions of the auctions (if you go that route) like does it work, the condition of the motor, etc..., get the serial # and look it up here
http://www.singerco.com/support/serial_numbers.html so you can date the machine and check that it is a 221 model, and look at the details of the machine. Hope this helps!