The switch in my 56 Nomad failed a couple years ago, while I was driving. I remember looking all over for a replacement and surprised they were not readily available. I finally took a chance from someone on eBay that said it was rebuilt. Fortunately it worked just fine.
Harder and harder to get good parts for our classics these days!
Good luck!

~ Victor
1941 3/4-Ton Pickup (in process). Read about it in the DITY Gallery
1955 Grumman Kurbside "Doughboy" 235/3 on tree w/ OD
1957 3100 - moved on
1959 C4500 Short Bus "Magic Bus" - moved on
1959 G3800 1 Ton Dually "Chief" - moved on
1958 C4400 Viking "Thor" ~ moved on to fellow Bolter