http://www.348-409.com/ Good spot for general information and occasionally parts for sale
http://www.409chevyperformance.com/E...rformance.html Have not dealt with them but seem to specialize in 348/409 stuff
http://www.nationalimpala.com/ Another good spot for general information and occasionally parts for sale
http://www.show-cars.com/ Mostly reproduction stuff.
As always you can look in Hemmings or other similar publications.
Verne - you have any other suggestions?