DuraLite in Riverton Ct 888-432-8797 will make you elements to order and is the single best source of them I know of.
Controllers
***********
Dwyer (Love) controllers is one supplier
www.love-control.com
Fuji
www.fujielectric.com
Digitry
www.digitry.com
Relays
*************8
Continental Industries int
www.cicontrols.com/contact
Payne Engineering
www.payneng.com
As well as Graingers and McMaster Carr
The book you have bought from Henry Halem "Glassnotes" will have extensive sources of suppliers in the back.