I remember seeing an article or write-up on repairing them, most times the toggle breaks off and somebody found a cheap donor switch for the toggle, and figured out how to disassemble the defrost switch to replace the toggle....
I remember reading it (because I have a switch somewhere with the toggle broken off) but damned if I can remember where I read it.
1972 Ford Mustang Mach 1 bright red, standard black interior,pb,ps
gauge package.rim blow steering wheel,15" magnum 500s,351 C 2bbl running a 4bbl Holley 600,MSD 6a with stock distributor and Pertronix,Comp cam mild grind, The Engine(rebuilt by me in 2002 for the second time the first rebuild I did was stock in 1995) made 305hp and 358 lb ft on the dyno. 9" 2.75 rear end,Global west sub frame connectors,620 front coils.Rear defroster. My parents bought my car brand new the year before I was born. I cherish it like my child.
I am interested in finding a replacement as well. Mine works but the lever portion has been broken off since I was a child. I never asked my parents how it happened. Replacing it has never made it on to the "to do" list.