I like sew classic too, and vintagesingerparts.
and for featherweights, mostly,
I also like Nova Montgomery's site:
https://www.novamontgomery.com/
oh and these too :
https://singer-featherweight.com/
and this one is good for featherweight decals:
https://www.singerdecals.com/221-222/
edit: I also came across these interesting links -resources for sewing machines:
http://www.doubleveil.net/zssmp/resources.htm
http://www.sewingmachineparts.net/