I have been looking for knife switches for a while. I come from AM broadcast where antenna contactors like this are common. http://www.kintronic.com/products/components/contactors/r-f-contactors/rfc-40-20-1-110-contactor.html
The problem is they are expensive. I asked why they didn't make a less expensive model. In thinking it over, it is clear that they sell less of the more expensive contactors. I did find this source:http://www.filnor.com/tech/literature/knifeswitch/Knife-Switch-Catalog-Full.pdf
I did come across DPDT knife switches that are used in emerging countries for their utility connections but are made in China.http://www.aliexpress.com/item/Heavy-Duty-2Poles-Double-Throw-DPDT-30A-Safety-Knife-Blade-Disconnect-Switches/601956280.html
This i more like it!!!
With the orange cover off they are either a plastic or ceramic base with reasonable quality copper switch parts. I have several on order.