Serial Numbers: http://www.singerco.com/support/serial_numbers.html
Parts / Supplies: http://sewingmachine221sale.bizland.com/store/index.html
221 Parts: http://www.221parts.com/
lady has ordered from this site. Good service.
This is more about garment sewing, but she handles FW parts and accessories.
Graham Forsdyke: http://www.singer-featherweight.com/index.html
Graham is located in England, and is one of the experts on FWs
Nova Montgomery: http://www.novamontgomery.com/
Nova is located in Texas. Quilter posted this note took a FW care and maintenance class from her.
Dave McCallum: http://www.featherweight221.com/fwrx/index.html
Dave is located in Washington state. He has a comprehensive book and DVD with step by step care and maintenance instructions. I would recommend you getting one or both.
Glenn Williams: http://pages.suddenlink.net/joyof301s/glenn.htm